Scope 3 · Category 3 · Well-to-Tank
Scope 3 Cat 3 Well-to-Tank Fuel Calculator (DEFRA WTT 2025)
Compute the upstream CO2e embedded in the fuels you burn — the well-to-tank emissions that sit in Scope 3, Category 3, not in Scope 1. DEFRA 2026 WTT-Fuels factors, reported as a separate inventory line per the GHG Protocol Scope 3 Standard.
Well-to-Tank (WTT) emissions are the upstream emissions generated to extract, refine, and deliver a fuel before it is combusted. They are distinct from the combustion (tank-to-wheel) emissions and are reported under Scope 3, Category 3 — “Fuel- and energy-related activities not included in Scope 1 or Scope 2.”
Core formula (DEFRA WTT-Fuels, as published):
WTT emissions (tCO₂e) = [Quantity × DEFRA WTT factor (kg CO₂e/unit)] ÷ 1,000
DEFRA publishes a WTT-Fuels factor table alongside its Scope 1 combustion factors, on the same unit basis (per kWh, per litre, per tonne). The WTT factor is a single pre-aggregated CO₂e value per unit — the calculator consumes it directly. The oxidation factor does not apply: upstream emissions occur during extraction and supply regardless of how completely the fuel is later burned. There is no AR5/AR6 disclosure toggle on this calculator — DEFRA’s WTT factors are pre-aggregated at AR5 GWP-100 by construction, the same basis the Scope 1 combustion factors inherit (see editorial basis reconciliation).
Scope boundary: This calculator covers fuel well-to-tank only (natural gas, diesel, LPG, and other liquid/gaseous fuels for which DEFRA publishes a WTT-Fuels factor). Out of scope — use the dedicated calculators: upstream emissions of purchased grid electricity (generation WTT) and transmission & distribution losses are separate Scope 3 Category 3 sub-lines with their own factor families; they are not computed here.
DEFRA 2026 WTT factor set, AR5 GWP-100 (aggregate CO₂e — no per-gas decomposition published).
WTW comparison adds Scope 1 combustion context — does not replace it.
Annualised: result × (12 ÷ period months).
Audit mode exposes per-line factor provenance for verification.
Add fuel lines above and click Calculate
Portfolio rollup, per-fuel contribution table, audit trail, and optional Well-to-Wheel lifecycle comparison appear after calculation.
Results are indicative, intended for Scope 3 Category 3.1 (Upstream emissions of purchased fuels) screening and order-of-magnitude estimates. For CDP, SBTi, CSRD, or ISO 14064 disclosure, validate factors against the primary DEFRA dataset, document your full Scope 3 inventory boundary, and report Cat 3.1 as a separate inventory line — do not net against Scope 1 combustion. AR5 GWP-100 is the DEFRA WTT publication basis; AR6 alternates are not published for upstream emissions.
Most organisations report the emissions from burning fuel and stop there. But every litre of diesel and every kilowatt-hour of gas carried a carbon cost long before it reached the meter — extraction, refining, and transport all happened upstream, and the GHG Protocol places that cost squarely in your Scope 3 inventory.
Omit well-to-tank and your fuel footprint is understated by roughly a sixth for gas and a quarter for diesel — a gap auditors increasingly expect to see closed.
Well-to-tank (WTT) emissions are the upstream CO₂e from extracting, refining, and delivering a fuel before combustion. They are reported under Scope 3, Category 3 — separately from the Scope 1 combustion total. For UK natural gas, WTT adds roughly 16.6% on top of the combustion figure.
On the Scope 1 stationary combustion calculator, well-to-tank is computed as a secondary companion to the main combustion figure. This calculator makes WTT the primary output — for organisations building out a complete Scope 3 inventory rather than verifying a single Scope 1 number. The methodology is identical; the framing is Scope 3-first.
Read Full WTT Methodology →Related Calculators
What Well-to-Tank Emissions Are — and Why They Sit in Scope 3 Category 3
Well-to-tank (WTT) emissions are the greenhouse gases released to bring a fuel from its source to the point of use. For a litre of diesel that means crude extraction, transport to a refinery, refining, and distribution to the forecourt or storage tank. For natural gas it means extraction at the wellhead, processing, and transmission through the pipeline network. All of this happens before the fuel is combusted — and all of it is upstream of the reporting organisation.
The Fuel Lifecycle: Well-to-Tank, Tank-to-Wheel, Well-to-Wheel
The full lifecycle of a combusted fuel splits into two stages. Well-to-tank (WTT) is everything up to the point the fuel enters your tank or supply. Tank-to-wheel (TTW) is the combustion itself — the emissions released when the fuel is burned in your boiler, furnace, or engine. Added together they form well-to-wheel (WTW), the total cradle-to-combustion footprint of the fuel.
Think of a litre of diesel as having two carbon price tags. One is paid when you burn it — that’s your Scope 1 combustion figure. The other was paid before it ever reached you, by the companies that drilled, refined, and shipped it — that’s well-to-tank. You don’t control those upstream emissions, but the GHG Protocol still expects you to count them, because your demand for the fuel caused them. They land in Scope 3, Category 3.
Why Upstream Fuel Is Scope 3 Category 3 — Not Scope 1 or Scope 2
The GHG Protocol Scope 3 Standard defines Category 3 as “fuel- and energy-related activities not included in Scope 1 or Scope 2.” Combustion of the fuel in equipment you own or control is Scope 1. The upstream emissions from producing that same fuel are not under your operational control — they belong to your suppliers — so they cannot sit in Scope 1. They are not purchased electricity or heat, so they are not Scope 2 either. Category 3 is the designated home for these upstream fuel emissions.
This is a boundary distinction with real reporting consequences. Pulling WTT into the Scope 1 total inflates your direct emissions and misrepresents what you control; omitting it entirely leaves a Scope 3 gap that a reviewer will identify. The correct treatment is a separate inventory line within Scope 3 Category 3, computed in parallel and reported alongside the Scope 1 combustion figure.
Included vs. Excluded on This Calculator
| Included in this calculator | Excluded — use the dedicated tool |
|---|---|
| WTT of natural gas, diesel, LPG, and other fuels with a published DEFRA WTT-Fuels factor | WTT of purchased grid electricity (upstream generation) — Scope 3 Cat 3, separate factor family |
| Upstream extraction, refining, processing, and distribution of the fuel | Transmission & distribution (T&D) losses on purchased electricity — Scope 3 Cat 3, separate calculation |
| Reported as a standalone Scope 3 Category 3 inventory line | Combustion (tank-to-wheel) emissions — that is Scope 1, see the stationary and mobile combustion calculators |
| Fuel quantities in the fuel’s native unit (kWh, litres, tonnes) | Biogenic-fuel upstream emissions — report separately per GHG Protocol Chapter 9 |
How the Calculation Works — DEFRA WTT 2025
The Core Formula
DEFRA publishes a dedicated WTT-Fuels factor table as part of its annual GHG Conversion Factors release. Each fuel carries a WTT factor on the same unit basis as its combustion factor — per kWh for gas, per litre for diesel and LPG, per tonne for solid fuels. The factor is a single pre-aggregated CO₂e value, so the calculation is a direct multiply: quantity times factor, divided by 1,000 to convert kilograms to tonnes.
Why There Is No AR5/AR6 Toggle Here
The Scope 1 stationary combustion calculator offers a dual-mode AR5/AR6 disclosure, because there are contexts where you reweight DEFRA’s published components at AR6 GWP-100 for science-based-target work. This WTT calculator deliberately does not. DEFRA’s WTT-Fuels factors are pre-aggregated CO₂e values constructed at AR5 GWP-100, and the per-gas decomposition needed to reweight them is not separately published for the WTT table. The factor is consumed as DEFRA constructs it. This matches the basis reconciliation rule applied site-wide: DEFRA-sourced fuel factors carry AR5 internally by design, and that asymmetry is intentional, not an inconsistency to be corrected.
Do not apply the oxidation factor to WTT. Oxidation completeness describes how thoroughly fuel burns at the point of use — it has no bearing on upstream extraction and refining emissions, which occur whether or not the fuel is later combusted efficiently. The oxidation factor belongs to the Scope 1 combustion calculation only.
What the Result Panel Shows
The calculator returns the WTT emissions in tonnes CO₂e for the quantity entered, labelled explicitly as a Scope 3 Category 3 line. Where the same fuel and quantity have a known Scope 1 combustion figure, the panel also expresses WTT as a percentage of that combustion total — the “uplift” your full fuel footprint carries once upstream emissions are included. The JSON export records the fuel, quantity, WTT factor value, factor source, and MasterBrain version for the audit trail.
Worked Example — Natural Gas, 4,847 kWh, Reconciled to the Scope 1 Page
This example uses the same 4,847 kWh of natural gas as Example 1 on the Scope 1 stationary combustion calculator, so the two pages reconcile exactly. The Scope 1 page reports this fuel’s combustion figure as 0.884 tCO₂e and its WTT companion as 0.146 tCO₂e; this calculator produces that same 0.146 tCO₂e WTT figure as its primary output.
WTT as a Share of the Fuel Footprint — By Fuel Type
The size of the well-to-tank uplift depends on the fuel. Gaseous and liquid fossil fuels carry meaningfully different upstream burdens relative to their combustion emissions. The figures below express the WTT factor as a percentage of the corresponding Scope 1 combustion factor — the proportional uplift your fuel footprint gains once upstream emissions are included.
Natural gas: 0.03021 ÷ 0.18231 = 16.6%. Diesel: 0.61101 ÷ 2.58354 = 23.7%. Both WTT factors are DEFRA 2026 WTT-Fuels values; both combustion factors are DEFRA 2026 (AR5 GWP-100). Bar widths are indicative, scaled for legibility.
If you already have your Scope 1 fuel combustion total, a quick sense-check is that natural gas WTT adds roughly a sixth and diesel roughly a quarter. A WTT line that comes out near zero, or larger than the combustion figure itself, signals a unit error or a wrong factor — trace it back before reporting.
Fuel-Specific Guidance — Factors, Use Cases, Common Mistakes
Natural Gas
Natural gas carries an upstream methane burden from extraction, processing, and pipeline transmission. The DEFRA 2026 WTT-Fuels factor is 0.03021 kg CO₂e/kWh (gross CV), roughly 16.6% of the combustion factor of 0.18231 kg CO₂e/kWh. For a site already reporting gas combustion under Scope 1, the WTT line is the single most material Scope 3 Category 3 entry from on-site fuel. Match the calculator unit to your billing unit precisely — UK bills typically headline kWh with m³ in finer print.
Diesel / Gas Oil
Diesel’s upstream burden is proportionally larger than gas because crude extraction and refining are energy-intensive. The DEFRA 2026 WTT-Fuels factor for diesel (average biofuel blend) is 0.61101 kg CO₂e/litre, about 23.7% of the combustion factor of 2.58354 kg CO₂e/litre. Diesel WTT is the dominant Scope 3 Category 3 fuel line for sites running standby generators or red-diesel plant. Watch for barrel/litre and gallon/litre confusion at the source document: one US barrel is 158.987 litres, one US gallon is 3.785 litres.
LPG and Other Fuels
LPG (and propane/butane) also carry a DEFRA WTT-Fuels factor, on a per-litre basis consistent with the combustion factor. The calculator reads the published LPG WTT value from MasterBrain at runtime rather than from a figure fixed in this prose — we hold no verified LPG WTT number, so it is deliberately not stated here to avoid asserting an unverified value. Where a fuel has no DEFRA WTT-Fuels factor at all (for example, the solid coal grades), the calculator suppresses the WTT line and the audit trail records the suppression; a Scope 3 Category 3 figure for that fuel should be sourced separately if material.
Reporting the well-to-wheel total (combustion + WTT) as a single Scope 1 figure. WTT is Scope 3 Category 3 and must be on its own line. Summing the two collapses a scope boundary the GHG Protocol requires you to maintain, and a reviewer will flag the inflated Scope 1 number.
How This Pairs With Your Scope 1 Inventory
Well-to-tank is the natural companion to fuel combustion. Every fuel you report under Scope 1 — whether burned in fixed equipment (stationary combustion) or in your own vehicles and plant (mobile combustion) — carries a parallel WTT line in Scope 3 Category 3. A complete fuel footprint reports both.
The workflow is straightforward: calculate the Scope 1 combustion figure on the stationary combustion calculator or the mobile combustion calculator, then bring the same fuel quantities here to produce the matching WTT line. Because both tools draw their factors from the same MasterBrain release, the figures reconcile — as the worked example above demonstrates against the stationary page. The result is a defensible pair of inventory lines: combustion in Scope 1, upstream fuel in Scope 3 Category 3, never commingled.
Stationary fuel
Boilers, furnaces, generators. Scope 1 combustion on the stationary calculator; WTT line here.
Mobile fuel
Own fleet, vessels, off-road plant. Scope 1 combustion on the mobile calculator; WTT line here.
Purchased electricity
Generation WTT and T&D losses are separate Scope 3 Cat 3 sub-lines — covered by the dedicated calculators, not this one.
Audit Checklist — What Gets Flagged on WTT Reporting
Third-party verification of a Scope 3 Category 3 inventory traces each fuel line from activity data through to the reported tCO₂e, confirming the boundary, the factor source, and the GWP basis. The recurring findings on well-to-tank reporting are below.
Regulatory Context — SECR, CSRD/ESRS E1, Singapore, Voluntary
UK — SECR and the DEFRA WTT Table
SECR mandates Scope 1 and Scope 2 reporting and encourages material Scope 3. DEFRA publishes the WTT-Fuels factors precisely so that UK reporters can quantify fuel-related Scope 3 Category 3 emissions on a consistent national basis. Where an organisation reports Scope 3, the fuel WTT line is among the most readily quantified entries, because the activity data is identical to the Scope 1 fuel data already collected. The factors are published by DESNZ (formerly BEIS) on a gross calorific value basis and updated annually each June.
EU — CSRD / ESRS E1
Under CSRD and ESRS E1, in-scope undertakings must disclose gross Scope 3 greenhouse-gas emissions, with fuel- and energy-related activities (the GHG Protocol Category 3 equivalent) expected where material. Well-to-tank fuel emissions are a standard component of that disclosure. The calculator’s JSON export provides the factor provenance and calculation chain that an ESRS E1 assurance engagement will trace.
Voluntary — CDP and SBTi
For CDP respondents and organisations setting science-based targets, fuel-related upstream emissions are part of a complete Scope 3 footprint. Because DEFRA’s WTT factors are constructed at AR5 and many inventories are kept at AR6 GWP-100, document the basis in your methodology notes. The drift between AR5 and AR6 for these pre-aggregated factors is small but non-zero; stating the basis explicitly avoids a consistency question during validation.
Singapore
Singapore’s Carbon Pricing Act, administered by the NEA, applies to large direct emitters; well-to-tank emissions are upstream Scope 3 and therefore outside the direct-emissions tax base, but they remain part of a complete corporate inventory for voluntary disclosure and target-setting. Verify factor selection against the NEA-approved tables for your reporting year before finalising any regulatory submission.
Data Sources, Factor Versioning, and Update Transparency
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 DEFRA Well-to-Tank (WTT) emission factors dataset.
Emission Factor Provenance
DEFRA 2026 GHG Conversion Factors, WTT-Fuels table (DESNZ, June 2026) is the source for every factor on this calculator. The values are pre-aggregated CO₂e numbers constructed at AR5 GWP-100, on the same unit basis as the corresponding combustion factors. MasterBrain stores the WTT factors under the fuels well-to-tank keyspace; the calculator reads the published value at runtime, with a built-in fallback if live data is unavailable.
GWP Basis
The WTT-Fuels factors inherit AR5 GWP-100 (CH₄ = 28; N₂O = 265) from DEFRA’s construction. There is no Engineering-mode reweight on this calculator, because DEFRA does not publish the per-gas decomposition for the WTT table that a reweight would require. If your wider inventory is framed at AR6, note the WTT line’s AR5 basis in your methodology documentation rather than attempting to reweight a pre-aggregated value.
Version History and Update Schedule
This calculator’s WTT factor data is sourced from MasterBrain v2026.284, last reviewed May 2026. DEFRA conversion factors — including the WTT-Fuels table — are updated annually each June; this calculator updates within 30 days of each DEFRA release via MasterBrain. The data version badge in the calculator footer reflects the live MasterBrain version in use. The DEFRA emission factors data page carries the published factor set for reference.
What’s Next? Completing Scope 3 Category 3
You have completed the fuel well-to-tank line of Scope 3 Category 3. Category 3 has two further sub-lines for organisations that purchase grid electricity — both handled by dedicated calculators so each reads its own factor family correctly. Once every line is logged, the GHG Inventory Aggregator rolls Category 3 together with all your other Scope 1, 2 and 3 sources into one auditable corporate carbon footprint.
The GHG Protocol requires Scope 1 and Scope 2 as a minimum; a complete fuel footprint reports the Category 3 well-to-tank line alongside them.
Frequently Asked Questions
Scope 3, Category 3. Combustion of the fuel in equipment you own or control is Scope 1; the upstream emissions from extracting, refining, and delivering that fuel are not under your control and belong to your suppliers, so they sit in Scope 3. Category 3 — “fuel- and energy-related activities not included in Scope 1 or Scope 2” — is the GHG Protocol’s designated home for them.
No. WTT is reported as a separate Scope 3 Category 3 inventory line, never summed into Scope 1. The combustion figure and the WTT figure are kept on distinct scope lines. If you want a combined cradle-to-combustion view, that is the well-to-wheel total — useful as supplementary information, but the formal inventory keeps the two scopes apart.
It depends on the fuel. For UK natural gas the DEFRA 2026 WTT factor (0.03021 kg CO₂e/kWh) is about 16.6% of the combustion factor (0.18231 kg CO₂e/kWh). For diesel the WTT factor (0.61101 kg CO₂e/litre) is about 23.7% of the combustion factor (2.58354 kg CO₂e/litre). Liquid fuels generally carry a larger upstream uplift than gas because extraction and refining are energy-intensive.
No — this calculator covers fuel well-to-tank only. Upstream electricity generation (grid WTT) and transmission & distribution losses are also Scope 3 Category 3, but they use entirely separate factor families and are handled by dedicated calculators. Using a fuel WTT factor for electricity would produce a wrong figure, so the boundary is kept strict here.
The Scope 1 combustion calculator can reweight DEFRA’s published components at AR6 GWP-100 because the per-gas decomposition is available for the combustion factors. DEFRA does not publish the equivalent decomposition for its WTT-Fuels table, so there is nothing to reweight — the WTT factor is a single pre-aggregated CO₂e value at AR5 GWP-100, consumed as published. If your inventory is framed at AR6, note the WTT line’s AR5 basis in your methodology documentation.
No. The oxidation factor describes how completely fuel burns at the point of use — a combustion parameter. Well-to-tank emissions occur upstream during extraction and refining, regardless of how the fuel is later burned, so the oxidation factor has no bearing on them. It belongs to the Scope 1 combustion calculation only.
Yes, by design. Both calculators draw their WTT-Fuels factors from the same MasterBrain release, so the same fuel and quantity produce the same WTT figure on both pages. For 4,847 kWh of natural gas, both report 0.146 tCO₂e. The Scope 1 page computes WTT as a secondary companion to its combustion output; this page makes WTT the primary result for Scope 3-first inventory building. The number is identical.
Where DEFRA does not publish a WTT-Fuels factor for a fuel (for example, the solid coal grades), the calculator suppresses the WTT line and records the suppression in the audit trail rather than estimating a value. If that fuel’s upstream emissions are material to your inventory, source a Scope 3 Category 3 figure from another recognised dataset and document it separately.
Methodology Notes and Limitations
Fuel WTT only. This calculator computes the upstream well-to-tank emissions of combusted fuels. Grid-electricity upstream generation and transmission & distribution losses — also Scope 3 Category 3 — are out of scope and handled by separate calculators with their own factor families.
Factor averaging. DEFRA WTT-Fuels factors are national averages across supply chains and do not reflect a specific supplier’s upstream intensity. For organisations with supplier-specific upstream data, that primary data is preferable where the GHG Protocol Scope 3 Standard’s data-quality hierarchy calls for it.
AR5 basis. WTT-Fuels factors are pre-aggregated at AR5 GWP-100 by DEFRA construction. No AR6 reweight is offered because the per-gas decomposition is not separately published for the WTT table. Document the basis in inventories framed at AR6.
Fuels without a WTT factor. Where MasterBrain has no DEFRA WTT-Fuels entry for a fuel, the WTT line is suppressed and the audit trail records it. A figure should be sourced separately if material.
No site-specific verification. This calculator is a calculation aid, not a measurement system. For regulatory submissions requiring site-specific accuracy, independent verification against primary data is required.