Whole-Business · Scope 1 + 2 + 3 Quick-Start
Small Business Carbon Footprint Calculator (Whole-Business Quick-Start)
Estimate your whole-business carbon footprint across Scope 1, Scope 2, and Scope 3 from seven activity modules — energy, fuel, travel, commuting, and purchased goods — using live DEFRA 2026 and US EPA spend-based emission factors, with per-employee intensity and a measured-versus-estimated data-confidence score. A screening tool built on the GHG Protocol Corporate Standard, not an audit-grade inventory.
Calculation formula (per activity line):
tCO₂e = Activity data × Emission factor ÷ 1000
The calculator runs that one multiplication for every activity line you enter, then sums the lines into Scope 1, Scope 2, and Scope 3 subtotals and a whole-business total. Activity data is the physical quantity of something your business did — kilowatt-hours of electricity, litres of fuel, passenger-kilometres of rail travel — and the emission factor converts that quantity into carbon-dioxide-equivalent. Nothing about the arithmetic is complex; the work is in getting the activity data and matching it to the right factor, both of which the calculator handles at runtime.
Two input modes, chosen per module. Every module can be entered in one of two ways. Measured mode uses your own data — the kWh from your electricity bill, the litres from your fuel receipts, the spend from your accounts — and produces the defensible, reproducible figure. Estimated mode applies a provisional sector intensity where you do not yet hold the underlying data, so you can see a whole-business shape before every number is collected. Estimated figures are engineering starting points, not measured results and not a peer benchmark; the calculator flags every module’s mode and reports an overall data-confidence percentage so a reader can see how much of the total is measured versus estimated.
Activity data × emission factor, resolved live. Emission factors are not hard-coded into the page. Each line resolves at runtime from MasterBrain V3, so a result always reflects the current factor set rather than a value frozen at publish time. For UK businesses the fuel, vehicle, travel, and commuting factors come from DEFRA 2026; electricity uses the location-based grid factor for the country you select; and purchased goods and services use a spend-based factor read from the US EPA Supply Chain dataset.
A whole-business screen, not a full inventory. This is a quick-start tool. It covers seven activity modules — the emissions sources that dominate a typical small business — and deliberately leaves out several categories that need their own treatment. Water, waste, and the deeper Scope 3 categories are out of scope here and belong in the GHG Inventory Aggregator; refrigerants and other fluorinated gases go to the F-gas Inventory Aggregator. Leaving these out is deliberate — a focused screen you can finish in minutes is more useful as a starting point than a full inventory you abandon halfway.
Mixed GWP basis — stated plainly. The activity-based factors (fuels, vehicles, travel, commuting, grid electricity) are DEFRA 2026 on an AR5 GWP-100 basis. The spend-based factor for purchased goods and services is US EPA Supply Chain data, also on an AR5 GWP-100 basis. Both sides of the calculation therefore share one GWP edition, so a whole-business total does not mix bases. (The EPA set was labelled AR6 here until August 2026 — our labelling error, corrected in MasterBrain v2026.110, with no change to any factor value.) The difference is immaterial at screening resolution, but it is real, and both the calculator and this page surface it rather than hiding it.
A screening aid, not a compliance output. The calculator makes no compliance claim. It produces a screening-grade estimate to help a small business understand the shape of its footprint and where to act first — it is not an audit-grade inventory, an assurance opinion, or a determination of any reporting obligation. Where a formal figure is needed, the screen is the starting point, not the deliverable.
Your profile powers the Estimated path and the per-employee / per-revenue intensities. Nothing is required — the footprint builds as you fill it in.
Scope 1Direct — fuel you burn on-site & in your vehicles
Scope 2Energy you buy — purchased electricity
Scope 3Value chain — travel, commuting & purchases
Water and waste are out of this quick-start — add them in the GHG Inventory Aggregator. Refrigerant leakage is Scope 1 — use the F-gas calculator.
Audit mode adds the full per-line calculation table — every factor key, source and figure.
Pick your country and industry, then add any activity — the rest is estimated for you
A whole-business Scope 1+2+3 total, scope split, per-employee intensity, a data-confidence readout, insights and an audit trail appear as soon as you enter your first figure.
This is a transparent GreenCalculus screening aid for a whole-business carbon footprint under the GHG Protocol Corporate Standard and Corporate Value Chain (Scope 3) Standard. Where you enter activity data, emission factors resolve live from the GreenCalculus MasterBrain — every such line is source-stamped and citable. The optional Estimated path derives activity from indicative industry benchmarks and is intended for a first-pass screen, not disclosure. It is not a certification, not a full GHG inventory, and not a substitute for independent validation/verification (e.g. under ISO 14064-3). Spend-based lines use US EPA supply-chain factors (per USD purchaser price); enter spend in USD or convert. Water, waste and refrigerants are out of scope here.
Most small businesses have never measured their carbon footprint, and the reason is rarely reluctance — it is that the standard tools are built for corporations with sustainability teams. A ten-person consultancy does not have Scope 3 category-15 financed emissions or a global facilities inventory. It has an electricity bill, a gas bill, maybe a company car, some train tickets, staff who drive to work, and a list of things it buys. That is the whole footprint, and it can be estimated in an afternoon.
This calculator is built for exactly that. It takes seven activity modules — the sources that make up almost all of a small business’s emissions — and turns them into a Scope 1 + 2 + 3 footprint with a per-employee intensity and an honest data-confidence score. It is a screening tool: fast, transparent, and clear about what it does not cover, so you get a defensible first number and a clear sense of where to act.
A small business’s carbon footprint is the sum of its Scope 1 emissions (fuel it burns on-site and in company vehicles), Scope 2 (electricity it buys), and Scope 3 (business travel, employee commuting, and purchased goods and services). Each source is calculated as activity data × emission factor: kWh, litres, kilometres, or spend, multiplied by the relevant carbon factor. For most small businesses, Scope 3 — and purchased goods and services in particular — is the largest share, often around two-thirds of the total, even though it is the part the business controls least directly.
What this calculator measures — a whole-business screen
This calculator estimates the operational carbon footprint of a small business across all three GHG Protocol scopes, from seven activity modules that between them capture almost all of a typical small business’s emissions. It is a whole-business screen: broad enough to give you a real Scope 1 + 2 + 3 total, focused enough to complete quickly, and honest about the handful of sources it deliberately leaves to specialised tools.
The seven modules
The calculator accepts seven activity modules, each mapped to the scope it belongs in. Every module can be entered in Measured mode (your own data) or Estimated mode (a provisional sector figure).
| Module | Scope | Typical small-business example |
|---|---|---|
| On-site heating fuel (gas / oil / LPG) | Scope 1 | Gas boiler heating an office or workshop |
| Company-vehicle fuel (litres) | Scope 1 | Diesel or petrol burned by owned or leased vehicles |
| Purchased electricity | Scope 2 | Grid electricity for lighting, equipment, and appliances |
| Business travel — air | Scope 3 (Cat 6) | Flights for client work or conferences |
| Business travel — ground (rail / car / taxi) | Scope 3 (Cat 6) | Train travel, mileage claims, taxis |
| Employee commuting | Scope 3 (Cat 7) | Staff travel between home and workplace |
| Purchased goods & services (spend-based) | Scope 3 (Cat 1) | Everything the business buys, estimated from spend |
What’s deliberately out of scope — and where it goes
Four things are intentionally excluded, because each is better handled by a tool built for it. Stating the boundary is a feature, not a gap: a screen that tries to cover everything shallowly is less useful than one that covers the dominant sources well and routes the rest cleanly.
| Out of scope here | Why | Where it belongs |
|---|---|---|
| Refrigerants and other F-gases | Fugitive-gas accounting needs charge/leak-rate logic, not activity × factor | F-gas Inventory Aggregator |
| Water and waste | Separate factor sets and treatment pathways; minor for most small businesses | GHG Inventory Aggregator |
| Deeper Scope 3 categories (capital goods, upstream transport, use of sold products, etc.) | Category-by-category work beyond a quick-start screen | GHG Inventory Aggregator |
| Financed emissions (Scope 3 Cat 15) | Applies to financial institutions, not typical small businesses | The PCAF calculator cluster |
“Quick-start” means this is a screening tool, not an audit-grade inventory. It is designed to give a small business a defensible first footprint and a clear sense of where its emissions sit — fast enough that you actually finish it. When you need a complete, category-by-category inventory or a formal disclosure, this screen is the on-ramp, and the GHG Inventory Aggregator and ISO 14064-1 Inventory Calculator are the next step.
How the calculation works — activity data × emission factor
Every line in the calculator reduces to one multiplication, run for each activity and summed by scope:
tCO₂e = Activity data × Emission factor ÷ 1000
Activity data is a physical quantity — kilowatt-hours, litres, kilometres, passenger-kilometres, or, for purchased goods, an amount of spend. The emission factor converts that quantity into kilograms of carbon-dioxide-equivalent, and dividing by 1,000 expresses the result in tonnes. The arithmetic is trivial; the value of the tool is in resolving the right factor for each activity automatically, so you never have to look one up.
The two input routes
Activity-based (higher fidelity)
Enter the physical quantity directly — kWh of electricity, litres of fuel, kilometres travelled. The factor is a physical emission factor (kg CO₂e per unit of energy or distance), so the result reflects what the business actually did. This is the route for energy, fuel, travel, and commuting, and it is the more accurate of the two wherever the underlying data exists.
Spend-based (broad coverage)
For purchased goods and services, physical data on thousands of purchases is impractical, so the calculator uses a spend-based factor: emissions per unit of currency spent in a category. It trades precision for coverage — one number for everything the business buys — and is the standard first-pass approach for Scope 3 Category 1. For a fuller treatment, see the Scope 3 Category 1 Spend-Based Calculator.
Measured and Estimated modes
Independently of the activity-versus-spend distinction, each module can be entered in Measured mode (your own data) or Estimated mode (a provisional sector intensity). Measured mode is what makes a result reproducible and defensible; Estimated mode lets you see the shape of a whole-business footprint before you have collected every number. The calculator reports a data-confidence percentage — the share of the total that rests on measured rather than estimated inputs — so the honesty of the number is visible on its face. The worked example below runs entirely in Measured mode, at 100% data confidence.
Start in Estimated mode across all seven modules to get a whole-business shape in a few minutes, then replace estimates with measured data one module at a time — beginning with the biggest. Because the modules are independent, you can lift your data-confidence score steadily without ever restarting. On most small businesses, measuring the top two or three modules moves the confidence score more than measuring the other four combined.
The three scopes for a small business
The GHG Protocol splits emissions into three scopes by how directly the business controls them. All three matter, but for a small business they behave very differently in size and in how much you can do about them.
Scope 1 — direct emissions you burn
Fuel combusted by sources the business owns or controls. For a small business this is almost always two things: heating fuel burned on-site (typically a gas boiler) and fuel burned by company vehicles. If your business rents a serviced office and has no vehicles, your Scope 1 may be zero. Scope 1 is the most directly controllable scope — you can switch a boiler or electrify a vehicle — but it is often not the largest.
- On-site fuel — gas, oil, or LPG for heating, measured in kWh or litres.
- Company vehicles — diesel or petrol, measured in litres.
Scope 2 — the electricity you buy
Purchased electricity for lighting, equipment, and appliances. The calculator uses a location-based grid factor for the country you select, so the same consumption produces different emissions in different countries as their grids differ in carbon intensity. In the UK the grid factor has fallen sharply as electricity has decarbonised, so Scope 2 shrinks year on year even with no change in consumption. The same grid-factor logic underlies the Scope 2 Electricity Calculator.
Scope 3 — everything else in your value chain
Indirect emissions from activities the business causes but does not own. This screen covers three Scope 3 categories that dominate small-business value chains: business travel (Cat 6), employee commuting (Cat 7), and purchased goods and services (Cat 1). For most small businesses this is the largest scope by a wide margin — and purchased goods and services is usually the single biggest line in the entire footprint, precisely because it captures everything the business buys.
The instinct to stop at Scopes 1 and 2 — the gas bill and the electricity bill, because they are the numbers you hold — misses the majority of a typical small business’s footprint. Scope 3 is harder to measure and less directly controllable, which is exactly why it gets skipped, and exactly why skipping it produces a number that is both too low and pointed at the wrong levers. A footprint that ignores what you buy and how staff travel is not a small-business footprint; it is a utility-bill summary.
Inputs this calculator needs — and where to find them
The calculation is one multiplication per line; the real task is gathering the activity data. The table below lists what each module needs and where a small business typically finds it. In every case, if you do not yet hold the data, Estimated mode lets you proceed and come back later.
| Module | Unit | Where to find it (Measured) | If you don’t have it (Estimated) |
|---|---|---|---|
| On-site heating fuel | kWh or litres | Annual gas/oil/LPG bill or supplier statement | Sector intensity by floor area |
| Company-vehicle fuel | Litres | Fuel-card statements or expense records | Estimated from mileage and vehicle type |
| Purchased electricity | kWh | Annual electricity bill or half-hourly meter data | Sector intensity by floor area or headcount |
| Business travel — air | Passenger-km or route | Travel booking records or expense claims | Estimated from headcount and role mix |
| Business travel — ground | Passenger-km or km | Rail tickets, mileage claims, taxi receipts | Estimated from headcount |
| Employee commuting | km (by mode) | Staff commuting survey | Estimated from headcount and default commute |
| Purchased goods & services | Spend (USD) | Annual accounts / procurement ledger by category | Estimated from turnover-linked ratios |
Three documents get most small businesses to a measured footprint: the annual electricity bill, the annual gas bill, and the year’s accounts (for both fuel/travel expenses and purchased-goods spend). A short staff commuting survey fills the last gap. If you gather only those, you can run five of the seven modules in Measured mode — which typically covers the large majority of the footprint.
Worked example — a 10-person professional-services business
This example reproduces exactly against the live calculator. It takes a UK professional-services business with 10 full-time employees and enters six lines across all three scopes — five activity lines plus one spend line — every one in Measured mode, so the whole result is reproducible from the inputs. Each line is the same operation: the activity quantity multiplied by its emission factor, divided by 1,000 to convert kilograms to tonnes.
The six input lines
| Source | Scope | Activity | MasterBrain factor (v2026.21) | Factor | tCO₂e |
|---|---|---|---|---|---|
| Purchased electricity | 2 | 15,000 kWh | grid.gbr.electricity.location_based |
0.13096 | 1.96440 |
| On-site heating (natural gas) | 1 | 20,000 kWh (gross CV) | fuels.gbr.natural_gas.kwh_gcv |
0.18231 | 3.64620 |
| Company vehicle (diesel) | 1 | 1,200 litres | mobile_combustion.diesel_average_biofuel.per_litre |
2.58354 | 3.10025 |
| Business travel — rail | 3 (Cat 6) | 8,000 passenger-km | business_travel.land.rail.national_rail |
0.03092 | 0.24736 |
| Employee commuting | 3 (Cat 7) | 40,000 km (petrol car) | commuting.car.size.average.petrol |
0.16152 | 6.46080 |
| Purchased goods & services | 3 (Cat 1) | USD 120,000 | spend_based.us.naics3.541.professional_scientific_and_technical_services |
0.089878 | 10.78536 |
The activity lines (electricity, gas, diesel, rail, commuting) use DEFRA 2026 factors on an AR5 basis; the spend line uses the US EPA Supply Chain factor, which is also AR5, and is entered in US dollars because that is the factor’s denominator. Both sides share one GWP edition.
How one line resolves — the spend line in full
Take the largest single line, purchased goods and services, to make the formula concrete. The business spent USD 120,000 on professional and technical services over the year. The spend-based factor for that category is 0.089878 kg CO₂e per US dollar (2022 purchaser price). So: 120,000 × 0.089878 = 10,785.36 kg, which is 10.78536 tCO₂e. The same operation runs on every line, and the six lines sum to the scope subtotals below.
Result — as the engine outputs it
| Scope | What it captures here | tCO₂e | Share of total |
|---|---|---|---|
| Scope 1 | On-site gas heating + company diesel vehicle | 6.75 | 26% |
| Scope 2 | Purchased electricity | 1.96 | 7% |
| Scope 3 | Rail travel + commuting + purchased goods & services | 17.5 | ≈67% |
| Total | Whole-business footprint | 26.2 | 100% |
The whole-business footprint is 26.2 tCO₂e, or 2.62 tCO₂e per employee across the 10 FTE. Because every line was entered in Measured mode, the data-confidence reading is 100% measured — no line rests on a sector estimate.
Scope 3 is about two-thirds of this business’s footprint — ≈67% of the total — and purchased goods and services alone (10.79 tCO₂e) is larger than Scope 1 and Scope 2 combined (8.71 tCO₂e). This is the defining pattern of small-business footprints: the emissions are mostly in what you buy and how people travel, not in the gas meter and electricity bill you control directly. A footprint exercise that stops at Scopes 1 and 2 would miss the majority of this business’s impact.
The biggest number in a small business’s footprint is usually the one it never sees on a bill — what it buys.
Every factor above resolves live. You can reproduce any line against the API — GET /wp-json/greencalculus/v1/factors?key_prefix=<key> returns the factor value the calculator used.
Measured vs Estimated mode — which to use and why
The single biggest driver of a footprint’s trustworthiness is how much of it rests on measured data versus sector estimates. The two modes are not competitors — they are stages. Estimated mode gets you a shape; Measured mode gets you a defensible number. The calculator reports the mix as a data-confidence score so the distinction is never hidden.
| Dimension | Measured mode | Estimated mode |
|---|---|---|
| Input | Your own kWh, litres, km, or spend | A provisional sector intensity applied to a proxy (floor area, headcount, turnover) |
| Accuracy | Reflects what the business actually did | Indicative shape only — not a measurement, not a benchmark |
| Effort | Requires gathering bills, records, a commuting survey | Minimal — proceed with what you know |
| Data-confidence impact | Raises the confidence score | Lowers it — visibly, so the reader sees the reliance |
| When to use | The final footprint, and any figure you share | A first-pass shape, or a module you’ll return to |
Estimated-mode figures are engineering starting points, not peer benchmarks and not measured results. Do not present an Estimated-mode total, or the per-employee and per-revenue ratios derived from it, as a comparison against other businesses — they are your own provisional internal ratios, computed from generic sector intensities that have not been validated against a peer dataset. Treat any Estimated-mode number as a placeholder to be replaced, and never put one into an external disclosure without saying it is an estimate.
How your footprint compares — reading the number honestly
The first question most people ask on seeing their footprint is “is that normal?” It is the natural question, and it is the one that is hardest to answer well — so this section answers it honestly rather than with a false precision.
There is no reliable, publicly validated dataset of small-business carbon footprints segmented by sector and size that would let this tool tell you where you sit against your peers. Footprints vary enormously with business model — a consultancy that mostly buys professional services looks nothing like a workshop that runs machinery or a courier that runs vehicles — and headline “average small business emits X tonnes” figures collapse that variation into a number that is misleading for almost every individual business. Rather than present a fabricated benchmark table, this calculator reports your own internal ratios (per employee and per unit of revenue) and leaves external comparison to properly sourced sector studies where they exist.
What the per-employee and per-revenue intensities are good for is tracking your own business over time. A footprint of 2.62 tCO₂e per employee this year is a baseline; the same figure next year tells you whether you are improving, holding, or growing your way into more emissions — and that internal trend is far more decision-useful than a comparison against a sector “average” built on incompatible business models. Where you do want a peer comparison, look for a sector-specific study with a stated methodology rather than a single cross-economy average.
Your footprint’s most useful comparison is against your own previous year, not against a sector average. Intensity ratios (per employee, per unit revenue) are designed for exactly this: they normalise for growth, so a rising absolute footprint driven purely by hiring shows as a flat intensity. Set this year as the baseline and track the trend — that is where the signal is.
What to do with your result — reduction levers ranked by impact
A footprint is only useful if it points to action. The value of the scope breakdown is that it tells you where your emissions actually are, so you can start with the biggest lever rather than the most visible one. For most small businesses, the ranking below reflects where the tonnes sit — and, notably, the most impactful lever is usually the least obvious.
| Lever | Scope | Typical impact | Effort |
|---|---|---|---|
| Engage suppliers / shift procurement to lower-carbon options | Scope 3 | High — usually the largest line | Medium–high (ongoing) |
| Reduce and shift commuting (remote days, cycle schemes, EV support) | Scope 3 | High where staff drive | Medium |
| Cut business travel / shift air to rail | Scope 3 | Medium–high for travel-heavy firms | Low–medium |
| Switch heating fuel (gas boiler → heat pump) | Scope 1 | Medium — removes on-site combustion | High (capital) |
| Electrify company vehicles | Scope 1 | Medium where vehicles are used heavily | High (capital) |
| Reduce electricity use / improve efficiency | Scope 2 | Lower — grid already decarbonising | Low |
Two things stand out from this ranking for a typical small business. First, the biggest lever is usually procurement — the least visible part of the footprint, because it never appears on a utility bill. Second, the most visible action, switching to a green electricity tariff or cutting office energy use, is often one of the smaller levers, because Scope 2 is a small and shrinking share as the grid decarbonises. Acting on the footprint rather than on instinct means starting where the tonnes are.
Once you have a measured baseline and know where your emissions sit, the natural next step is a reduction target. The SBTi Near-Term Target Calculator takes an absolute-emissions baseline and derives a science-aligned reduction trajectory, and the broader SBTi Corporate Net-Zero Standard sets out the framework. A screening footprint is enough to start; a measured one is enough to commit to a target.
Reporting context — GHG Protocol, SECR, ISO 14064, PPN 006, SBTi
A small business rarely faces the mandatory reporting obligations that bind large companies, but several frameworks shape what a footprint should look like and when one becomes necessary. The overview below reflects the position as of July 2026; reporting rules move, so confirm the current legal position before relying on any of it for compliance. This calculator asserts no compliance outcome — it is a screening aid.
| Framework | What it is | Relevance to a small business |
|---|---|---|
| GHG Protocol Corporate Standard | The foundational carbon-accounting standard defining the three scopes | The methodology this calculator follows; the basis for essentially every other framework |
| GHG Protocol Scope 3 Standard | The detailed standard for value-chain (Scope 3) emissions across 15 categories | Defines the travel, commuting, and purchased-goods categories this screen covers |
| SECR (UK) | Streamlined Energy and Carbon Reporting — statutory annual energy/carbon disclosure | Generally binds only large companies; most small businesses are out of scope (see below) |
| ISO 14064-1 | The international standard for organisational GHG inventories | The route to a formal, verifiable inventory when a screen is not enough |
| PPN 006 (UK, formerly PPN 06/21) | Procurement rule requiring a Carbon Reduction Plan to bid for major public contracts | Applies by contract value, not company size — can pull small suppliers in (see below) |
| SBTi Corporate Net-Zero Standard | The framework for validating science-aligned reduction targets | The next step after measuring — turns a baseline into a target |
SECR — most small businesses are out of scope
The UK’s Streamlined Energy and Carbon Reporting regime requires annual energy and carbon disclosure in a company’s report, but it targets large organisations. As of July 2026, an unquoted company or LLP is caught only if it meets at least two of three thresholds — 250 or more employees, turnover of £36 million or more, or a balance sheet total of £18 million or more — while all quoted companies are in scope regardless of size. A typical small business meets none of these and has no SECR obligation, though a very low-energy user below 40 MWh a year would in any case qualify for a de minimis exemption. The UK Sustainability Reporting Standards, in development to build on and eventually supersede SECR, may change this picture — confirm the current position before assuming you are out of scope.
PPN 006 — the procurement trigger that can catch small suppliers
PPN 006 — renamed from PPN 06/21 in February 2025 to align with the Procurement Act 2023, with the substance unchanged — requires suppliers bidding for major central-government contracts to publish a Carbon Reduction Plan committing to net zero by 2050. Crucially, it applies by contract value (generally £5 million or more per year), not by the size of the bidding business, and there is no small-business exemption. A small firm bidding for in-scope public work therefore needs a compliant plan built on a GHG Protocol footprint covering Scope 1, Scope 2, and a defined subset of Scope 3 — and in practice many public frameworks and NHS procurement now ask for one more broadly. If public-sector work is on your horizon, a measured footprint is the foundation of the plan.
Reporting and procurement rules are fast-moving. The thresholds, names, and scope above are current as of July 2026, but SECR, the incoming UK Sustainability Reporting Standards, and PPN 006 have all changed in recent years and continue to evolve. Confirm the current legal position with the relevant official guidance before treating any of this as settled, and record the assumptions you relied on. This calculator produces a screening footprint; it does not determine whether any obligation applies to you.
Data sources, emission factors and versioning
The complete underlying reference — every factor in this section, versioned with full source provenance and downloadable as CSV with a citable Zenodo DOI — is published as the UK spend-based GHG intensity by SIC section dataset.
Every factor resolves live from MasterBrain V3 at the moment you run the calculator, so a result reflects the current factor set rather than a value frozen when this page was written. The worked example above was computed against MasterBrain version v2026.21 (updated 2 July 2026). Two factor families feed the tool: DEFRA 2026 for the activity-based lines and US EPA Supply Chain factors for the spend-based line.
Activity-based factors — DEFRA 2026
| Activity | MasterBrain key | Factor | Basis | GWP basis |
|---|---|---|---|---|
| Electricity (UK) | grid.gbr.electricity.location_based |
0.13096 kg CO₂e/kWh | National grid average, location-based | AR5 GWP-100 |
| Natural gas (UK) | fuels.gbr.natural_gas.kwh_gcv |
0.18231 kg CO₂e/kWh | Gross calorific value | AR5 GWP-100 |
| Diesel (company vehicle) | mobile_combustion.diesel_average_biofuel.per_litre |
2.58354 kg CO₂e/litre | Average biofuel blend, per litre | AR5 GWP-100 |
| Rail (business travel) | business_travel.land.rail.national_rail |
0.03092 kg CO₂e/passenger-km | National rail, per passenger-km | AR5 GWP-100 |
| Car commuting (petrol) | commuting.car.size.average.petrol |
0.16152 kg CO₂e/km | Average car size, per km | AR5 GWP-100 |
Electricity uses a location-based grid factor keyed by country: the UK draws on DEFRA 2026, the US on EPA eGRID 2023, and other countries on Ember 2025. The same grid-factor logic underlies the Scope 2 Electricity Calculator. Note the UK grid factor is 0.13096 kg CO₂e/kWh under DEFRA 2026 — materially lower than earlier vintages as the grid has decarbonised, so a figure computed against an older factor set is not comparable line-for-line.
Spend-based factor — US EPA Supply Chain v1.3.0
Purchased goods and services use the US EPA Supply Chain GHG Emission Factors, version 1.3.0, indexed by three-digit NAICS category and expressed per 2022 US dollar of purchaser price on an AR5 GWP-100 basis. This is why spend is entered in US dollars rather than pounds. The choice is deliberate: DEFRA’s UK spend-based rows are gross-value-added intensities — a different accounting basis — so they are not interchangeable with the EPA purchaser-price factors and are not used here. The spend-based approach is the lowest-fidelity route in the tool; for a fuller treatment of spend-based Category 1 accounting, see the Scope 3 Category 1 Spend-Based Calculator.
The activity lines and the spend line sit on different GWP vintages — DEFRA 2026 activity factors are AR5, the EPA spend factor is AR6. At screening resolution the difference is immaterial, but it means a whole-business total is not internally single-basis. If you later rebuild the inventory to assurance grade, reconcile everything to one GWP basis first. The calculator surfaces this mixed-basis note, and any figure taken from it into a formal disclosure should carry the same caveat.
Versioning and update cadence
DEFRA updates its UK factors annually, typically in mid-year; EPA and grid sources update on their own cycles. Because factors resolve live, the calculator always uses the current MasterBrain vintage, and each result carries the MasterBrain version stamp (v2026.21 for the worked example) so a figure computed against one vintage and the same inputs computed against a later one are distinguishable in any restatement. The tool does not maintain your activity data — you supply the kWh, litres, distances, and spend; the calculator supplies and applies the factors.
Common mistakes and limitations
A screening footprint is easy to run and easy to misread. The issues below are the ones that most often distort a small-business result or lead it to be over-claimed — worth checking before you rely on or share a number.
01 — Stopping at Scopes 1 and 2
Reporting only the gas and electricity bill because those are the numbers you hold omits the majority of a typical small business’s footprint. Scope 3 — travel, commuting, and purchased goods — is usually the largest scope. A Scope 1 + 2 figure is not a footprint; it is a utility summary, and it points at the wrong levers.
02 — Treating an Estimated-mode total as measured
Estimated mode gives a shape, not a measurement. Presenting an estimated total — or the per-employee ratio derived from it — as your actual footprint overstates its reliability. Check the data-confidence score and replace estimates with your own data before sharing a number.
03 — Reading intensity ratios as peer benchmarks
The per-employee and per-revenue figures are your own internal ratios, not a comparison against other businesses. There is no validated peer dataset behind them. Use them to track your own trend over time, not to claim you are above or below a sector average.
04 — Mixing currencies or units in the spend line
The spend module expects US dollars, because the EPA factors are per-USD. Entering pounds or euros without converting inflates or deflates the largest line in the footprint. Convert to USD first, and keep the FX rate and date on record.
05 — Expecting F-gas, water, or waste to be included
These are deliberately out of scope. A business with significant refrigeration or process water that assumes this screen captured them will understate its footprint. Route refrigerants to the F-gas Inventory Aggregator and the rest to the GHG Inventory Aggregator.
06 — Using a screen where an inventory is required
This tool makes no compliance claim. Using its output directly in a statutory disclosure, a Carbon Reduction Plan, or an assurance filing without rebuilding to the relevant standard risks a non-compliant submission. Treat the screen as the starting point and step up to ISO 14064-1 or the full aggregator when a formal figure is needed.
07 — Comparing figures across factor vintages
The UK grid factor and other factors change year to year. Comparing this year’s footprint against a prior year computed on an older factor set mixes real change with factor change. Note the MasterBrain version stamp, and for a like-for-like trend, recompute the baseline on the current factors.
08 — Ignoring the mixed GWP basis in formal use
The activity lines are AR5 and the spend line is AR6. Immaterial for screening, but if the number feeds a disclosure that specifies a single GWP basis, the total needs reconciling first. Carry the mixed-basis caveat with any figure you export.
Frequently asked questions
Add up the emissions from each source the business is responsible for, calculated as activity data × emission factor. Scope 1 is fuel burned on-site and in company vehicles (kWh or litres × a fuel factor); Scope 2 is purchased electricity (kWh × a grid factor); Scope 3 is business travel, employee commuting, and purchased goods and services (distance or spend × the relevant factor). This calculator does that across seven modules and sums them into a whole-business total with a per-employee intensity. For most small businesses the largest share is Scope 3, and purchased goods and services is usually the single biggest line.
There is no reliable single figure, and this calculator deliberately does not quote one. Small-business footprints vary enormously with business model — a consultancy that buys professional services looks nothing like a workshop running machinery or a courier running vehicles — so a cross-economy “average” is misleading for almost every individual business. In the worked example on this page, a 10-person professional-services firm came to 26.2 tCO₂e, or 2.62 tCO₂e per employee, but that reflects its specific mix and is not a benchmark. The most useful comparison is against your own previous year, not a sector average.
Most do not. The UK’s SECR regime binds quoted companies of any size and large unquoted companies or LLPs — those meeting at least two of three thresholds (250+ employees, £36m+ turnover, £18m+ balance sheet) as of July 2026. A typical small business meets none and has no SECR obligation. The main way a small business gets pulled in is procurement: PPN 006 requires a Carbon Reduction Plan to bid for major public contracts (generally £5m+/year), and that applies by contract value, not company size. Reporting rules change, so confirm the current position before relying on this.
Because Scope 3 captures everything the business buys and all the travel it causes, while Scope 1 and 2 capture only the fuel and electricity it uses directly. Purchased goods and services alone often exceeds Scope 1 and Scope 2 combined — in the worked example it was 10.79 tCO₂e against 8.71 tCO₂e for Scopes 1 and 2 together. The irony is that Scope 3 is the part a business controls least directly and sees least clearly, because it never appears on a utility bill, which is exactly why footprints that stop at the bills understate the total and aim at the wrong levers.
Yes. Every module can run in Estimated mode, which applies a provisional sector figure to a proxy like floor area, headcount, or turnover, so you can get a whole-business shape in minutes without any bills. Then replace estimates with your own data one module at a time, biggest first — the modules are independent, so you never restart, and the data-confidence score rises as you go. Just don’t treat an Estimated-mode total as a measured figure or share it as one; it is a placeholder to be replaced.
Four things are deliberately out of scope: refrigerants and other F-gases (use the F-gas Inventory Aggregator), water and waste, the deeper Scope 3 categories beyond travel, commuting and purchased goods (both use the GHG Inventory Aggregator), and financed emissions, which apply to financial institutions. This is a quick-start screen built around the seven modules that dominate a typical small business’s footprint; the boundary is intentional, so the tool stays fast and honest rather than shallow across everything.
Because the spend-based factors come from the US EPA Supply Chain dataset, which is expressed per 2022 US dollar of purchaser price. The alternative UK spend factors are built on a different accounting basis (gross value added), so they are not interchangeable, and the tool uses the EPA set for consistency. Convert your purchased-goods spend to US dollars before entering it, and keep the exchange rate and date on record. This also means the spend line sits on an AR6 GWP basis while the activity lines are AR5 — immaterial for screening, but noted for transparency.
It is a screening estimate, not an audit-grade inventory, and it makes no compliance claim. It is ideal for understanding your footprint and deciding where to act, and a measured-mode run is a solid foundation for a Carbon Reduction Plan or a reduction target. But for a statutory disclosure, a formal PPN 006 submission, or an assurance filing, you should rebuild to the relevant standard — the ISO 14064-1 Inventory Calculator for a verifiable inventory, or the GHG Inventory Aggregator for a complete Scope 1 + 2 + 3 inventory. Use this screen as the on-ramp.
Activity factors (fuels, company vehicles, business travel, commuting) come from DEFRA 2026 on an AR5 GWP-100 basis; electricity uses a location-based grid factor by country (UK DEFRA 2026, US EPA eGRID 2023, others Ember 2025); and the purchased-goods spend factor comes from US EPA Supply Chain GHG Emission Factors v1.3.0 on an AR5 basis. All resolve live from MasterBrain at runtime, so a result always uses the current factor set, and each result carries a version stamp. Note the current UK grid factor is 0.13096 kg CO₂e/kWh — much lower than a few years ago as the grid has decarbonised.
Start where the tonnes are, which the scope breakdown shows you. For most small businesses the largest lever is procurement — engaging suppliers and shifting to lower-carbon purchases — followed by commuting and business travel, because those Scope 3 lines usually dominate. Switching heating fuel and electrifying vehicles cut Scope 1, and improving electricity efficiency cuts Scope 2, but Scope 2 is often a small and shrinking share as the grid decarbonises. The common mistake is to start with the most visible action (an office energy tweak) rather than the biggest one (what you buy). Once you have a baseline, the SBTi Near-Term Target Calculator helps turn it into a reduction target.
Methodology notes and limitations
Screening tool, not an inventory. This calculator produces a screening-grade estimate of a small business’s operational carbon footprint. It is not an audit-grade inventory, an assurance opinion, or a determination of any reporting obligation, and it makes no compliance claim. For a complete or verifiable inventory, use the GHG Inventory Aggregator or the ISO 14064-1 Inventory Calculator.
Coverage boundary. Seven activity modules only: on-site heating fuel and company-vehicle fuel (Scope 1); purchased electricity (Scope 2); business travel by air and ground, employee commuting, and purchased goods and services (Scope 3). Refrigerants and other F-gases (see the F-gas Inventory Aggregator), water, waste, the deeper Scope 3 categories, and financed emissions are out of scope.
Measured and Estimated modes. Each module can be entered with the business’s own data (Measured) or a provisional sector intensity (Estimated). Estimated-mode figures are engineering starting points, not measured results and not peer benchmarks; the per-employee and per-revenue ratios are the business’s own internal ratios, not external comparisons. The data-confidence percentage reports the measured share of the total.
Emission factors. Activity factors are DEFRA 2026 (AR5 GWP-100); electricity uses a location-based grid factor by country; the purchased-goods spend factor is US EPA Supply Chain v1.3.0 (AR5 GWP-100, per 2022 USD purchaser price). Factors resolve live from MasterBrain V3 at runtime, and each result carries the MasterBrain version stamp (v2026.21 for the worked example on this page).
Mixed GWP basis. The activity lines (AR5) and the spend line (AR6) sit on different GWP vintages. The difference is immaterial at screening resolution but real; a figure taken into a formal single-basis disclosure should be reconciled first. The calculator surfaces this note.
Spend entered in USD. The purchased-goods module expects US dollars because the EPA factors are per-USD; DEFRA’s GVA-based UK spend factors are on a different basis and are not used. Convert before entry and document the FX rate and date.
No FX conversion. The calculator does not convert currencies. Enter energy, fuel, and travel data in their physical units and spend in USD; the economic-intensity ratio assumes a consistent basis.
Inputs taken at face value. The calculator applies factors to the activity data you enter; it does not independently verify your kWh, litres, distances, or spend. The user is responsible for the accuracy and completeness of the inputs.
Reporting facts are time-stamped and fast-moving. SECR thresholds, the incoming UK Sustainability Reporting Standards, and PPN 006 (formerly PPN 06/21) are stated as of July 2026 and change frequently. They are provided for orientation, not as legal advice; confirm the current position with official guidance before relying on any of it for compliance, and record the assumptions used.
No assurance opinion. Results are estimates and do not constitute a PCAF or ISO assurance opinion. For a formal figure, rebuild to the relevant standard and have it reviewed by a qualified practitioner before use in any disclosure, tender, or target filing.