Entity footprint · Scope 1, 2 & 3
Office Carbon Footprint Calculator (Per Employee) — Scope 1, 2 & 3 Emissions
Estimate an office’s annual carbon footprint and its per-employee carbon intensity across all three scopes — stationary energy, refrigerants, water, waste, business travel, commuting, and homeworking — under the GHG Protocol Corporate Standard, with DEFRA 2026 activity factors and location-based grid electricity across ten countries.
What the calculator sums. An office footprint is the annual total of every emission source the office controls or causes, expressed in tonnes of CO₂-equivalent and then normalised to a per-employee intensity. The calculator groups sources into the three GHG Protocol scopes: Scope 1 (on-site natural-gas heating and refrigerant leakage), Scope 2 (purchased electricity, location-based), and Scope 3 (water, waste, business travel, employee commuting, homeworking, and a screening line for other purchased goods). Each source is an activity figure multiplied by an emission factor, divided by 1,000 to convert kg CO₂e to tonnes, and the lines are summed by scope and in total.
Per employee is the headline metric. Absolute tonnes tell you how large the office is; they do not tell you whether it is carbon-efficient. Dividing the total by full-time-equivalent headcount produces tonnes CO₂e per FTE — the metric that lets a 15-person studio and a 500-person head office be compared on the same axis, and the metric that moves when the office electrifies heating, switches to a cleaner grid, or shifts to hybrid working. Per-square-metre and per-£m-revenue intensities are also reported when floor area or revenue is supplied, but headcount is the default normaliser because it is the input every office can provide.
The emission factors, and their GWP basis. UK activity factors are read live from the MasterBrain against the DEFRA 2026 conversion-factor set, on AR5 GWP-100 — the basis DEFRA publishes on. Refrigerant global-warming potentials are the one exception: they are carried on AR6 GWP-100, following the F-gas convention. So the correct one-line statement of basis is that DEFRA 2026 activity factors are AR5 GWP-100 while refrigerant GWPs are AR6 — not that everything is AR5. Grid electricity is location-based in this version: the factor is the national grid average for the selected country, read by country code.
Two ways to enter energy. Electricity and gas each accept a measured mode (annual kWh from utility bills) and an estimated mode (floor area multiplied by a CIBSE TM46 building-energy benchmark of 95 kWh/m² electricity and 120 kWh/m² gas for a general office). Measured energy is the higher-confidence input; the estimate exists so an office that knows only its floor area can still produce a screening figure. Gas automatically adds a well-to-tank companion line in Scope 3 Category 3, capturing the upstream emissions of extracting and delivering the fuel.
Location-based only, in this version. Electricity is accounted location-based — the grid average. A market-based figure that reflects a green tariff, REC, or PPA is not entered here; renewable-electricity procurement is handled in the dedicated renewable procurement calculator. This calculator answers “what does the grid attribute to this office”, which is the figure most disclosure regimes require as the location-based baseline regardless of contractual instruments.
Confidence, not a data-quality score. The calculator weights each line by whether it was measured or estimated and reports a confidence band — High, Medium, or Screening. This is a screening-grade signal, not the formal five-level PCAF data quality score used in financed-emissions work. It exists to tell a reader how much of the total rests on meter readings versus benchmark estimates.
Where the boundary sits. This is an entity-level office screening tool, not a full corporate Scope 3 inventory. It covers the sources a typical office actually generates; it does not attempt the fifteen-category Scope 3 completeness a manufacturer or financial institution needs. When the office footprint is complete, the natural next step is the full-inventory Scope 1, 2 & 3 aggregator, and the source-specific calculators linked throughout this page for any line that needs greater depth.
Fill in the modules that apply — electricity and gas open by default. Enter metered kWh, or estimate from floor area. Each source shows its own subtotal, and the result updates live.
Audit mode adds the full per-line calculation table — every factor key, source and figure.
Enter your office electricity, gas and headcount to calculate
Add commuting, business travel, waste, water, refrigerants and homeworking for a full per-employee footprint. A scope split, confidence rating, audit trail and export appear instantly.
This is a transparent GreenCalculus screening aid for estimating an office’s operational carbon footprint per employee under the GHG Protocol Corporate & Corporate Value Chain (Scope 3) Standards. Emission factors are resolved live from the GreenCalculus MasterBrain — grid electricity per country, and gas, water, waste, business travel, commuting and homeworking on DEFRA 2026 (UK) factors, with CIBSE TM46 benchmarks for floor-area estimates. Every activity line is source-stamped and citable. It is not a certification and not a substitute for independent verification (e.g. ISO 14064-3). Scope 2 is reported location-based; add market-based figures via the renewable-procurement calculator. Outside the UK, non-grid factors apply as a UK proxy — substitute local factors before disclosure.
An office does not smoke like a factory or roll like a fleet, so its carbon footprint is easy to underestimate. But the electricity keeping the lights and laptops on, the gas heating the floors, the refrigerant leaking from the air-conditioning, the waste going to landfill, and — usually the largest single line — the daily commute of everyone who works there all add up to a real and measurable annual total.
This calculator assembles that total across all three GHG Protocol scopes and divides it by headcount, so the number you take away is not just how many tonnes the office emits, but how many tonnes it emits per person — the figure that tells you whether your office is efficient and where the reductions actually live.
An office carbon footprint is the annual sum of its energy, refrigerant, water, waste, travel, and commuting emissions in tonnes CO₂e, divided by full-time-equivalent headcount to give tonnes CO₂e per employee. Electricity and commuting are typically the two largest lines.
What an office footprint covers across the three scopes
An office generates emissions in all three GHG Protocol scopes, and the balance between them is characteristic: unlike an industrial site, where Scope 1 process emissions dominate, a typical office’s footprint is led by Scope 2 electricity and by the Scope 3 emissions of getting people to and from the building. Understanding which scope a source sits in matters because disclosure regimes report by scope, and because the reduction levers differ scope by scope.
The three-scope split for a typical office
| Scope | Office sources in this calculator | Why it sits here |
|---|---|---|
| Scope 1 — direct | On-site natural-gas heating and hot water; refrigerant leakage from air-conditioning and chillers | Emissions from sources the office owns or controls — fuel burnt on site, and F-gases that escape from on-site equipment |
| Scope 2 — purchased energy | Purchased grid electricity for lighting, plant, servers, and equipment (location-based) | Emissions from generating the electricity the office buys — produced off-site, but caused by the office’s consumption |
| Scope 3 — value chain | Employee commuting, homeworking, business travel, waste, water, the gas well-to-tank companion, and other purchased goods (screening) | Indirect emissions the office causes but does not own — most notably the daily travel of its workforce |
What is in scope, and what belongs in a dedicated calculator
| Covered in this calculator | Better handled elsewhere |
|---|---|
| On-site natural-gas heating, entered as measured kWh or estimated from floor area | Non-gas heating fuels — oil, LPG, biomass — see the Scope 1 stationary combustion calculator (this tool is natural-gas-only in v1) |
| Purchased grid electricity, location-based, across ten countries | Market-based electricity reflecting a green tariff, REC, or PPA — see the renewable procurement calculator |
| Refrigerant leakage from office HVAC, by refrigerant type and charge | A whole-organisation F-gas inventory across many assets — see the refrigerant leakage calculator for depth |
| Employee commuting and homeworking, as a screening line by mode | A full commuting survey with mode-share modelling — see the commuting & homeworking calculator |
| Office waste by stream and disposal route | A detailed multi-site waste inventory — see the waste streams calculator |
For most offices the two largest lines are purchased electricity (Scope 2) and employee commuting (Scope 3). On-site gas is material where heating is gas-fired; refrigerants, water, and waste are usually smaller but are included because they are cheap to estimate and because leaving them out understates the total. The calculator is a screening tool that gets an office to a defensible number across all three scopes — not a substitute for a full fifteen-category Scope 3 inventory.
How the calculation works — activity data to per-employee intensity
Every line in the calculator reduces to the same operation, run for each source and summed:
Line emissions (tCO₂e) = Activity data × Emission factor ÷ 1,000
Activity data is the physical quantity — kWh of electricity, kWh of gas, kilometres commuted, tonnes of waste, m³ of water, kilograms of refrigerant lost. The emission factor converts that quantity to kilograms of CO₂e; the division by 1,000 expresses the result in tonnes. The lines are then grouped into Scope 1, Scope 2, and Scope 3 subtotals, summed to a whole-office total, and divided by headcount.
The normalisation step — three intensity denominators
Per employee (headline)
Total tCO₂e ÷ full-time-equivalent headcount. This is the default intensity because headcount is the one input every office can supply, and because it makes offices of very different sizes directly comparable. If headcount is left blank or zero, the total still renders and the per-FTE figure simply shows a dash — the calculator never produces a spurious number.
Per square metre (optional)
Total tCO₂e ÷ floor area in m², reported only when floor area is entered. This is the intensity that maps onto building-energy benchmarks and is most useful for comparing the building itself rather than the organisation occupying it. Floor area also feeds the CIBSE estimate mode for energy.
Per £m revenue (optional)
Total tCO₂e ÷ annual revenue in £m, reported only when revenue is entered. This is the economic-intensity view familiar from SECR intensity ratios — useful for year-over-year trend reporting, less useful for comparing dissimilar organisations.
Use full-time-equivalent headcount, not raw headcount, for the per-employee figure. Two half-time staff are one FTE; counting them as two people understates the per-employee intensity and makes the office look more efficient than it is. Commuting and homeworking are annualised on a 45-working-week year — the calculator’s built-in constant — so a “days per week” input already accounts for holidays and typical absence.
The office emission sources in detail
The calculator groups office activity into modules. Electricity and gas are open by default because they are present in almost every office; the rest are collapsible and entered only where relevant. Each module writes to a scope and applies the appropriate factor.
Stationary energy — electricity and gas
Electricity is the office’s Scope 2 line: annual kWh multiplied by the location-based grid factor for the selected country. Gas is the Scope 1 heating line: annual kWh on a gross-calorific-value basis multiplied by the UK natural-gas factor, with an automatic well-to-tank companion added to Scope 3 Category 3 for the upstream fuel-supply emissions. Both accept measured kWh from bills or an estimate from floor area using the CIBSE TM46 general-office benchmark. The Scope 2 electricity calculator and Scope 1 combustion calculator carry the same factor logic if a line needs more granularity than this screening tool offers.
Refrigerants — the Scope 1 line offices forget
Air-conditioning and chillers leak fluorinated refrigerants, and because those gases have global-warming potentials in the hundreds or thousands, even a small annual leak is a non-trivial Scope 1 emission. The calculator takes the refrigerant type, the installed charge in kilograms, and an annual leak rate (defaulting to 15%), and multiplies the leaked mass by the refrigerant’s GWP. Refrigerant GWPs are carried on AR6 GWP-100 following the F-gas convention — the one basis exception on this page, and one governed by the EU F-gas Regulation.
Travel and people — commuting, homeworking, business travel
Commuting (Scope 3 Cat 7)
Per mode — car, bus, rail, metro, motorbike — entered as one-way distance, days per week, and number of employees. The calculator annualises on 45 working weeks and applies the DEFRA per-km factor for the mode. For most offices this is the single largest line, which is why it is worth entering by mode rather than as one blended average.
Homeworking (Scope 3 Cat 7)
The energy staff use working from home — heating, lighting, and equipment — captured as number of homeworkers, home days per week, and hours per day, multiplied by the DEFRA per-FTE-working-hour homeworking factor. Hybrid working shifts emissions out of the office and into this line rather than removing them.
Business travel (Scope 3 Cat 6)
Air (with radiative forcing applied), rail, car, taxi, coach, and ferry, entered as passenger-kilometres per year. Air travel dominates where it occurs — a handful of long-haul flights can outweigh a year of commuting for a small office. The air travel calculator handles complex itineraries in more detail.
Other purchased goods (Scope 3 Cat 1)
A single screening line entered directly in tCO₂e, for offices that have a spend-based estimate of purchased goods and services. This bridges to the spend-based Category 1 calculator for a proper spend-based build; here it exists so the figure can be included without being double-counted.
Water and waste
Water is a single Scope 3 line: mains supply in m³ per year, carrying both a supply factor and a wastewater-treatment factor. Waste is entered by stream — general and mixed commercial, paper and card, plastics, metal, glass, WEEE, food — and by disposal route — landfill, closed-loop recycling, combustion, composting, anaerobic digestion — because the route matters far more than the mass: a tonne of paper to landfill and a tonne to recycling carry very different factors. The waste streams calculator covers a detailed multi-site waste inventory.
Location-based vs market-based electricity for offices
Electricity is usually an office’s largest single line, and how it is accounted determines a large part of the total. The GHG Protocol Scope 2 Guidance defines two methods, and the difference matters for any office that buys green electricity.
| Dimension | Location-based (this calculator, v1) | Market-based (separate calculator) |
|---|---|---|
| Factor used | National grid average for the country | The emission rate of the electricity product contracted (green tariff, REC, PPA), or a residual mix |
| What it answers | What the physical grid attributes to this office’s consumption | What the office’s purchasing choices attribute to it |
| Effect of a green tariff | None — the grid average is unchanged by contracts | Can reduce the electricity line toward zero with a valid instrument |
| Where it lives at GreenCalculus | Here — location-based is the default baseline | Renewable procurement (REC/PPA) calculator |
Most disclosure regimes require the location-based figure to be reported regardless of any green-electricity contracts, because it reflects the physical grid and is not sensitive to the quality of contractual instruments. If your office holds a green tariff or PPA, report the location-based number here as your baseline, then compute the market-based figure separately — the two are complementary, not alternatives. For the full comparison, see location-based vs market-based Scope 2.
Why per employee is the right intensity metric
An absolute footprint answers “how big”, not “how efficient”. A 500-person head office will always emit more tonnes than a 15-person studio; that tells you nothing about which is better run. Normalising to intensity removes the size effect, and for an office the three candidate denominators — headcount, floor area, revenue — each answer a slightly different question.
Per employee — the organisation’s efficiency
Tonnes per FTE is the fairest cross-office comparison because an office exists to house people, and headcount is available everywhere. It responds directly to the levers that matter — cleaner electricity, electrified heating, hybrid working — and it is the number a workforce intuitively understands. This is the calculator’s headline.
Per square metre — the building’s efficiency
Tonnes per m² isolates the building’s performance from how densely it is occupied, which is why it maps onto building-energy benchmarks. A sparsely occupied office looks good per m² but poor per FTE; a densely packed one is the reverse. Useful, but it measures the building, not the organisation.
Per £m revenue — the economic view
Tonnes per £m is the economic-intensity ratio used in SECR reporting. It is well-suited to tracking one organisation’s trend over time, but it makes dissimilar organisations hard to compare because revenue per head varies enormously by sector.
Report per-employee intensity as your headline and per-m² alongside it where you have floor area. The pair separates two different questions a reader will ask — is the organisation efficient with its people, and is the building efficient with its space — and offices that improve on one but not the other are common and worth surfacing.
Inputs this calculator needs — and where to source them
Everything the calculator needs sits in systems the office already runs — HR, facilities, finance, and utility accounts. The table below lists the inputs that drive the result and where each is typically found.
| Input | Unit | Primary source | Fallback source |
|---|---|---|---|
| Employees (FTE) | Headcount | HR system — full-time-equivalent count | Payroll record |
| Electricity | kWh/yr | Utility bills or half-hourly meter data | Floor area × CIBSE TM46 benchmark (estimate mode) |
| Natural gas | kWh/yr (gross CV) | Gas utility bills | Floor area × CIBSE TM46 benchmark (estimate mode) |
| Floor area | m² | Lease or facilities record | Energy-performance certificate floor-area field |
| Commuting | km, days/week, staff count | Staff commuting survey | Postcode-to-office distance estimate by mode |
| Refrigerant charge | kg, % leak rate | HVAC maintenance / F-gas log | Equipment nameplate charge, default 15% leak rate |
| Waste | tonnes/yr by stream and route | Waste contractor duty-of-care reports | Bin-volume estimate |
| Water | m³/yr | Water utility bills | Occupancy × per-head water benchmark |
Start with the two big lines — electricity and commuting — before chasing the small ones. An office footprint is usually 60–80% those two sources, so a measured electricity figure and a reasonable commuting survey get you most of the way to a defensible number. Refrigerants, water, and waste refine the tail; they rarely change the headline. Enter what you can measure, estimate the rest, and let the confidence band tell your reader how much of the total is measured.
Benchmarks — what the data does and does not support
The most common question about an office footprint is “is my per-employee number good or bad?” — and the honest answer is that there is no authoritative, sourced tonnes-CO₂e-per-employee benchmark for offices to compare against. Published per-FTE carbon figures circulate widely, but they rest on undisclosed assumptions about grid factor, heating fuel, commuting mode, and floor-area basis, which makes them unreliable as a yardstick. GreenCalculus does not publish a per-employee CO₂e band it cannot source.
What is sourced is an energy-intensity benchmark. The CIBSE TM46 general-office benchmark defines a typical office’s annual energy use per square metre, and it is the same benchmark the calculator’s estimate mode uses. It is an energy figure, not a carbon figure — so it tells you whether your building’s kWh/m² is typical, which is a meaningful and defensible comparison, without pretending to a carbon benchmark that does not exist.
| CIBSE TM46 general office — energy intensity | Benchmark | Basis |
|---|---|---|
| Electricity | 95 kWh/m²/yr | CIBSE TM46 activity benchmark (general office) |
| Fossil-fuel (gas) heating | 120 kWh/m²/yr | CIBSE TM46 activity benchmark (general office) |
Treat any “average office emits X tonnes per employee” claim with caution — including ones you may have seen elsewhere. Without a stated grid factor, heating fuel, commuting-mode mix, and floor-area basis, a per-employee carbon figure is not comparable across offices, and publishing one as a benchmark would be a fabricated value. Compare your building’s energy against the CIBSE kWh/m² benchmark above, which is sourced; treat your per-employee carbon figure as an internal trend metric to improve against your own prior years, not against an external band. A sourced per-employee band would need a dataset that does not currently exist in our reference.
Related tool: The TM46 comparison is only as good as the inputs that place a building in its benchmark category — the EUI position checker tests which of those would distort it: category choice, floor area, separables and adjustments.
Worked example — a 15-FTE UK office
This example is the calculator’s shipped default and reproduces exactly against the live engine. It is a 15-FTE UK office with measured electricity and gas, a diesel-car commute for ten staff, and eight staff homeworking two days a week. Reporting currency and country are UK throughout, so the grid and gas factors are both MasterBrain-native. Every line is activity × factor ÷ 1,000, computed against MasterBrain v2026.13.
Inputs
| Line | Scope | Activity | Factor (kg CO₂e) | tCO₂e |
|---|---|---|---|---|
| Electricity (measured) | S2 | 40,000 kWh | 0.13096 /kWh | 5.2384 |
| Natural gas (measured) | S1 | 55,000 kWh | 0.18231 /kWh | 10.02705 |
| Gas — well-to-tank | S3 Cat 3 | 55,000 kWh | 0.03021 /kWh | 1.66155 |
| Commuting (car, avg diesel) | S3 Cat 7 | 54,000 km (12 × 2 × 5 × 45 × 10) | 0.17265 /km | 9.32310 |
| Homeworking | S3 Cat 7 | 5,760 FTE-hr (8 × 2 × 45 × 8) | 0.32393 /hr | 1.86584 |
The commuting activity is the largest single line despite being a screening estimate: ten staff each driving a 12-km one-way diesel commute, five days a week over 45 working weeks, is 54,000 km, and at the DEFRA average-diesel-car factor that is 9.32 tCO₂e. Gas heating is the second-largest at 10.03 tCO₂e in Scope 1, with its well-to-tank companion adding a further 1.66 in Scope 3. Electricity, on the current UK grid factor, is 5.24 tCO₂e — a reminder of how far the UK grid has decarbonised, since a decade ago the same 40,000 kWh would have carried roughly double the emissions.
Scope subtotals and the headline
| Scope | tCO₂e | Share of total |
|---|---|---|
| Scope 1 (gas + refrigerants) | 10.02705 | 35.7% |
| Scope 2 (electricity) | 5.2384 | 18.6% |
| Scope 3 (WTT + commuting + homeworking) | 12.85049 | 45.7% |
| Total | 28.11594 → displays 28.1 | 100% |
Two things are worth drawing out. First, Scope 3 is the largest scope at 45.7%, driven almost entirely by the commute — which is typical of offices and is why a commuting figure, even a rough one, cannot be omitted without materially understating the footprint. Second, the confidence is High because electricity and gas were entered as measured meter readings; had they been estimated from floor area, the confidence would drop and the reader would know the total rested more on benchmarks than on bills. The per-employee figure of 1.87 tCO₂e/FTE is the number to track over time — not against an external benchmark, which does not reliably exist, but against this office’s own future years as it electrifies heating or shifts commuting modes.
Reducing an office footprint — the highest-impact levers
Because the footprint concentrates in a few lines, so do the reductions. The levers below are ordered by typical impact for an office, and each maps to a scope and a source the calculator already surfaces.
Switch the commute (Scope 3, usually largest)
Commuting is the biggest lever precisely because it is the biggest line. Shifting car commutes to rail, cycling, or hybrid working days moves tonnes directly out of the total — though hybrid working shifts some of it into the homeworking line rather than eliminating it. Model both and net the change.
Electrify heating (Scope 1 → Scope 2)
Replacing gas heating with a heat pump moves the heating load from Scope 1 gas onto Scope 2 electricity — and on a decarbonising grid that is a large net reduction, because the grid factor keeps falling while the gas factor does not. It also removes the well-to-tank companion line.
Buy cleaner electricity (Scope 2)
A green tariff or PPA reduces the market-based electricity figure toward zero — accounted in the renewable procurement calculator, not here. The location-based baseline this calculator reports is unchanged by contracts, so report both: the physical baseline and the contractual reduction.
Fix refrigerant leaks (Scope 1)
Because refrigerant GWPs run into the thousands, tightening a leaking AC system or switching to a low-GWP refrigerant such as R-32 or R-1234yf can remove a surprisingly large Scope 1 line for a small office. Regular F-gas servicing is the cheapest carbon win most offices overlook.
The order matters: chase the commute and heating before the water cooler. An office that spends its effort on recycling and paper while ignoring a gas boiler and a car-dependent commute is optimising the tail and leaving the body of the footprint untouched. The per-scope split in the result panel tells you where the tonnes actually are — start there.
Reporting context — GHG Protocol, SECR, CSRD, ISO 14064-1
An office footprint feeds several disclosure regimes, depending on the organisation’s size and jurisdiction. The frameworks below are the ones an office-based organisation most commonly encounters.
| Framework | Role for an office footprint | Who it applies to |
|---|---|---|
| GHG Protocol Corporate Standard | The accounting foundation. Defines the three scopes, the operational boundary, and the activity × factor method this calculator implements. | The global baseline; referenced by nearly every other regime |
| UK SECR | Requires UK energy use and Scope 1 + 2 emissions plus an intensity ratio — the per-employee or per-£m figures this calculator produces map directly. | UK large companies and LLPs meeting the SECR thresholds |
| CSRD ESRS E1 | Requires Scope 1, 2, and material Scope 3 disclosure with intensity metrics. An office footprint is a component of the entity total. | Large EU and EU-operating companies, phased from 2024 |
| ISO 14064-1 | The organisational GHG inventory standard. Provides the quantification and reporting structure for a verifiable office or entity inventory. | Any organisation seeking a standardised, verifiable inventory |
For a full multi-year SECR intensity ratio, the SECR calculator assembles the required energy-and-emissions statement; for the complete entity inventory across all fifteen Scope 3 categories, the Scope 1, 2 & 3 aggregator is the next step up from this office screening tool.
Data sources, factor versioning, and update transparency
Emission factors and their basis
UK activity factors are read live from the MasterBrain against the DEFRA 2026 conversion-factor set. The basis statement matters and is often stated incorrectly: DEFRA 2026 activity factors are on AR5 GWP-100, which is the basis DEFRA publishes on, while refrigerant global-warming potentials are carried on AR6 GWP-100 following the F-gas convention. It is therefore wrong to describe the whole page as “AR5” — the accurate statement is DEFRA activity factors on AR5, refrigerant GWPs on AR6. Grid electricity is location-based, read by country code across the ten countries the calculator supports.
| Source | Basis | GWP basis | Covers |
|---|---|---|---|
| DEFRA 2026 (UK) | National grid average (location-based); gross-CV gas; per-km travel; per-tonne waste; water | AR5 GWP-100 | Electricity, gas, gas WTT, commuting, business travel, waste, water |
| Grid factor set (non-UK) | Location-based national grid average, by country code | Per dataset | Electricity for the other nine supported countries |
| F-gas refrigerant GWPs | Global-warming potential per refrigerant | AR6 GWP-100 (F-gas convention) | Refrigerant leakage (Scope 1) |
| CIBSE TM46 | General-office energy-intensity benchmark (95 kWh/m² elec, 120 kWh/m² gas) | Energy benchmark, not CO₂e | The estimate mode for electricity and gas |
Versioning and update cadence
DEFRA refreshes its UK conversion factors annually, and the grid factor in particular falls year over year as the grid decarbonises. The calculator stamps each result with the MasterBrain version it was computed against, so a figure computed on one vintage and the same office computed on a later vintage are distinguishable in restatement work. The same grid-factor logic underlies the Scope 2 electricity calculator; for a spend-based estimate of purchased goods where no physical data exists, see the spend-based Category 1 calculator.
What’s next — from office footprint to full inventory
An office footprint is a screening-grade entity total. Once it is in hand, the paths below deepen or extend it.
The full entity inventory
The Scope 1, 2 & 3 aggregator assembles a complete organisational inventory across all fifteen Scope 3 categories — the step up from this office-scoped screening tool.
Deepen the big lines
Take electricity into the Scope 2 calculator, gas into the Scope 1 combustion calculator, and commuting into the commuting & homeworking calculator for line-level depth.
Meet a disclosure obligation
For UK reporting, the SECR calculator builds the required energy-and-emissions statement and intensity ratio directly from the same underlying figures.
Set a reduction target
Once the baseline is complete, the SBTi near-term target calculator takes the absolute footprint and derives a science-aligned reduction trajectory.
The full methodological detail behind this calculator — the activity-factor chain, the confidence-band construction, the CIBSE estimate mode, and the working-week annualisation — is published on the paired office carbon footprint methodology page.
Frequently asked questions
There is no authoritative, sourced tonnes-CO₂e-per-employee benchmark for offices, and figures that circulate online rest on undisclosed assumptions about grid factor, heating fuel, commuting mode, and floor-area basis that make them unreliable as a yardstick. What is sourced is the CIBSE TM46 energy-intensity benchmark for a general office — 95 kWh/m² electricity and 120 kWh/m² gas — which lets you compare your building’s energy use per square metre against a defensible reference. Treat your own per-employee carbon figure as an internal trend metric to improve against your prior years, not against an external band.
All three. Scope 1 is on-site natural-gas heating and refrigerant leakage; Scope 2 is purchased grid electricity, accounted location-based; Scope 3 is employee commuting, homeworking, business travel, waste, water, the gas well-to-tank companion, and a screening line for other purchased goods. For a typical office the two largest lines are usually Scope 2 electricity and Scope 3 commuting, and Scope 3 is often the largest scope overall because of the commute.
This calculator uses location-based — the national grid average — because that is the baseline most disclosure regimes require regardless of any green-electricity contracts. If your office holds a green tariff, REC, or PPA, report the location-based figure here as your baseline and compute the market-based figure separately in the renewable procurement calculator. The two are complementary: location-based reflects the physical grid, market-based reflects your purchasing choices. See location-based vs market-based Scope 2 for the full comparison.
Use the estimate mode. Electricity and gas each accept a floor-area input that is multiplied by the CIBSE TM46 general-office benchmark — 95 kWh/m² for electricity and 120 kWh/m² for gas — to produce a screening estimate. It is lower confidence than a meter reading, and the result’s confidence band will reflect that, but it lets an office that knows only its floor area still produce a defensible number. Move to measured kWh from utility bills when you can.
Commuting is a Scope 3 Category 7 emission the office causes by requiring people to travel to it, and for most offices it is indeed the single largest line — in the worked example, ten staff driving a 12-km diesel commute five days a week produce 9.3 tCO₂e a year, more than the office’s electricity. Omitting it materially understates the footprint, which is why the calculator includes it even as a screening estimate by mode. Hybrid working shifts some of this emission into the homeworking line rather than eliminating it, so model both.
Yes, where the office runs air-conditioning or chillers. Fluorinated refrigerants have global-warming potentials in the hundreds or thousands, so even a small annual leak is a non-trivial Scope 1 emission. The calculator applies AR6 GWP-100 values to the leaked mass — this is the one basis exception on the page, following the F-gas convention, while the DEFRA activity factors are on AR5. Tightening a leaking system or switching to a low-GWP refrigerant is often the cheapest Scope 1 reduction available to a small office.
DEFRA 2026 activity factors — electricity, gas, travel, waste, water — are on AR5 GWP-100, which is the basis DEFRA publishes on. Refrigerant global-warming potentials are the exception: they are carried on AR6 GWP-100 following the F-gas convention. So the correct statement is that activity factors are AR5 and refrigerant GWPs are AR6 — not that the whole calculator is AR5. This mixed basis is by design and is not an inconsistency.
No. This is an entity-level office screening tool covering the sources a typical office generates; it does not attempt the fifteen-category Scope 3 completeness a manufacturer, retailer, or financial institution needs. It gets an office to a defensible cross-scope number quickly. When you need the full organisational inventory, the Scope 1, 2 & 3 aggregator is the next step, with the source-specific calculators linked throughout this page for any line needing depth.
It is a screening-grade signal of how much of the total rests on measured data versus estimates. Each line is weighted by whether it was measured (a meter reading) or estimated (a benchmark), and the tonnes-weighted result is reported as High, Medium, or Screening. In the worked example the band is High because electricity and gas were entered as measured meter readings. It is not the formal five-level PCAF data quality score used in financed-emissions accounting — it is a lighter-weight indicator for a screening tool.
Ten in this version: the UK, US, Ireland, Germany, France, Spain, Italy, the Netherlands, Australia, and Canada. The electricity factor is the location-based national grid average for the selected country. The non-grid factors — gas, travel, waste, water — are UK-native DEFRA values, so an office outside the UK gets a country-specific electricity figure but UK-basis factors for the other lines; for a fully localised non-UK footprint, use the country’s national factor sources for those lines.
Methodology notes and limitations
Screening scope. This calculator produces a screening-grade office footprint across Scope 1, 2, and 3 using the sources a typical office generates. It is not a full fifteen-category Scope 3 inventory and does not claim organisational completeness for organisations with significant upstream or downstream emissions beyond the office itself.
Electricity is location-based only. Version 1 accounts electricity at the national grid average. Market-based accounting reflecting a green tariff, REC, or PPA is not an input here; it is handled in the renewable procurement calculator. Report the location-based figure as the baseline regardless of contractual instruments.
Heating is natural gas only. Version 1 models on-site heating as natural gas. Oil, LPG, biomass, and district-heat systems are out of scope for this tool — use the Scope 1 stationary combustion calculator for other heating fuels.
GWP basis is mixed by design. DEFRA 2026 activity factors are on AR5 GWP-100; refrigerant GWPs are on AR6 GWP-100 per the F-gas convention. Describing the page as uniformly AR5 is incorrect. This asymmetry is intentional and follows the source conventions.
No sourced per-employee carbon benchmark. The calculator reports a per-FTE intensity but does not compare it against an external tonnes-per-employee band, because no authoritative, sourced band exists in our reference. The only sourced benchmark on this page is the CIBSE TM46 energy-intensity figure (95 kWh/m² electricity, 120 kWh/m² gas), which is an energy benchmark, not a carbon one. An in-calculator per-FTE band is deferred pending a sourced dataset.
Confidence band, not a data-quality score. The reported confidence (High / Medium / Screening) is a tonnes-weighted measured-versus-estimated signal, not the formal PCAF five-level data quality score. It communicates how much of the total rests on meter readings rather than benchmarks.
Inputs taken at face value. The calculator does not validate that entered energy, distances, or masses are correct — it applies the factor to what is entered. Commuting and homeworking are annualised on a 45-working-week year. The user is responsible for entering full-time-equivalent headcount and a consistent floor-area basis.
Non-UK offices. Only electricity is localised by country code. Gas, travel, waste, and water use UK-basis DEFRA factors, so a non-UK office receives a country-specific electricity figure but UK-basis factors for the other lines. For a fully localised non-UK footprint, substitute national factor sources for those lines.
No assurance opinion. Results are screening estimates and do not constitute an assurance opinion. They should be reviewed by a qualified practitioner before use in regulatory submissions. The full methodological detail is published on the paired office carbon footprint methodology page.