UK DEFRA Well-to-Tank (WTT) Emission Factors 2026 — Complete Upstream Fuel Dataset

Well-to-tank (WTT) factors quantify everything that happens to a fuel before you burn it — extraction, refining, processing and delivery to the point of use. Burning the fuel is a separate, larger number. This page publishes the complete UK DEFRA 2026 WTT dataset: 164 factors covering 31 fossil fuels, 19 bioenergy fuels and UK grid electricity generation, every one traced to its cell in the published DEFRA workbook.

WTT is the factor most often left out of a corporate inventory. It is not optional under the GHG Protocol: the upstream emissions of every fuel you burn and every unit of electricity you buy belong in Scope 3 Category 3 (fuel- and energy-related activities not already in Scope 1 or Scope 2). For a road-freight or heating-heavy business it typically adds 15–25% on top of the combustion total.

What well-to-tank measures

A litre of diesel in your tank has already caused emissions before your engine turns over. Crude oil had to be extracted and transported to a refinery; the refinery consumed energy and vented process emissions; the finished product was moved by pipeline, ship and road to a depot and then to the forecourt. WTT is the sum of all of that, expressed per unit of the finished fuel.

The boundary DEFRA applies is cradle to point of use. It includes:

• Extraction and production — drilling, mining, flaring, venting and fugitive losses at the wellhead or mine.
• Processing and refining — the energy and process emissions of turning crude or raw gas into a usable product.
• Transport and distribution — moving the fuel by pipeline, tanker, rail and road, including losses in transit.

It excludes the combustion itself, and it excludes the capital goods of the supply chain — the refinery, the pipeline and the tanker fleet are not amortised into the factor. Those belong in Scope 3 Category 2 if they are material to you.

Where WTT sits in the GHG Protocol

Every factor on this page maps to Scope 3 Category 3 — fuel- and energy-related activities not included in Scope 1 or Scope 2. The category exists precisely because the upstream half of your energy consumption is real, material and attributable to you, but is not an emission from a source you own or from electricity you purchased.

A complete Category 3 figure is the sum of three separate elements: fuel WTT, electricity generation WTT, and transmission & distribution losses (both the T&D energy itself and its own upstream). This page supplies the first two.

Fossil fuel factors

All 114 fossil-fuel factors below, in kg CO₂e per unit of fuel. A dash means DEFRA does not publish that fuel on that basis — solid fuels have no litre or cubic-metre figure, and only the two natural-gas entries carry a cubic-metre basis. Read the calorific-value warning in gross versus net before using any per-kWh column.

Bioenergy & biofuel factors

All 49 bioenergy factors, in kg CO₂e per unit of fuel. These are not zero and must not be treated as such: the memo-item rule for biogenic carbon applies to combustion of the biomass, not to the energy and emissions of producing, processing and transporting it. Units differ from the fossil table because DEFRA publishes bioenergy on a GJ, kg, litre, kWh and tonne basis rather than on gross/net calorific value.

Grid electricity factors

The upstream of the fuel burnt at UK power stations on your behalf, per kWh consumed. This sits alongside your Scope 2 generation figure, not instead of it, and it is separate again from transmission and distribution losses.

Gross versus net calorific value

Every per-kWh factor in the fossil table is published on two bases, and picking the wrong one is the most common quiet error on this dataset.

• Gross calorific value (GCV), or higher heating value. Counts the latent heat recovered when water vapour in the combustion products condenses. This is the UK convention — gas bills, DEFRA reporting guidance and UK boiler efficiencies are all quoted gross.
• Net calorific value (NCV), or lower heating value. Excludes that latent heat. This is the international and IPCC convention, and what most non-UK datasets use.

Because the same upstream emissions are divided by a larger energy denominator, the gross factor is always the smaller number. UK natural gas is 0.03021 kg CO₂e/kWh gross against 0.03347 net — an 11% difference that will silently misstate a gas-heavy inventory if the basis of your consumption data and the basis of your factor disagree.

Application — formulas & worked examples

WTT arithmetic is a single multiplication. The difficulty is never the formula; it is using the right factor on the right basis and putting the answer in the right scope.

WTT emissions (kg CO2e) = fuel quantity x WTT factor for that fuel and unit

Diesel in an owned fleet

A company burns 10,000 litres of 100% mineral diesel in vehicles it owns.

10,000 litres x 0.62409 kg CO2e/litre = 6,240.9 kg CO2e = 6.24 t CO2e  ->  Scope 3 Category 3

The combustion of that same diesel is a separate, larger figure and belongs in Scope 1. Reporting only the Scope 1 number leaves this 6.24 tonnes out of the inventory entirely.

Natural gas for heating

A site consumes 500,000 kWh of natural gas, metered on the UK gross basis.

500,000 kWh x 0.03021 kg CO2e/kWh (gross CV) = 15,105 kg CO2e = 15.1 t CO2e  ->  Scope 3 Category 3

Using the net-CV factor here instead would give 16.7 t — a 1.6 tonne overstatement created purely by a column choice.

Purchased electricity

A site imports 250,000 kWh from the UK grid.

250,000 kWh x 0.03682 kg CO2e/kWh = 9,205 kg CO2e = 9.21 t CO2e  ->  Scope 3 Category 3

This is the upstream of the fuel burnt at the power station, and it sits alongside — not instead of — the Scope 2 generation figure and the separate transmission & distribution loss element.

Calculators that use these factors

The worked examples above are automated in these GreenCalculus tools, which read this dataset live from the MasterBrain so results always reflect the current vintage:

• Scope 3 Category 3 well-to-tank calculator — the upstream WTT emissions of purchased fuel and electricity.
• Fleet carbon footprint calculator — fleet fuel use with its upstream WTT component.
• Mobile combustion calculator — the tank-to-wheel combustion companion to these WTT factors.
• Business travel (air) calculator — flights including their well-to-tank share.
• Train vs plane vs car calculator — modal comparison on a consistent WTT basis.

Common reporting errors

• Omitting WTT altogether. The most frequent error. A Scope 1 and Scope 2 inventory with no Category 3 line is incomplete, and it is the first thing an assurer checks once the obvious scopes reconcile.
• Reporting WTT inside Scope 1. Upstream emissions are not from a source you own or control. They belong in Scope 3 whatever the fuel.
• Applying a well-to-wheel factor and calling it Scope 1. WTW bundles the upstream in; splitting it back out afterwards is guesswork. Use the TTW factor for Scope 1 and the WTT factor here for Category 3.
• Mixing calorific bases. Gross-basis consumption data against a net-basis factor, or the reverse. See gross versus net.
• Treating bioenergy WTT as zero. Biogenic combustion CO₂ is a memo item; the emissions of growing, harvesting, processing and transporting the biofuel are not, and they are often substantial relative to the fuel’s own combustion figure.
• Double-counting electricity. Generation WTT, T&D losses and the T&D losses’ own upstream are three distinct elements. Adding a blended “electricity lifecycle” factor on top of a Scope 2 figure usually counts at least one of them twice.

Methodology, boundaries & uncertainty

GWP basis. Every factor is published by DEFRA as an aggregate CO₂e value on the IPCC AR5 100-year basis. DEFRA does not publish a per-gas decomposition for upstream emissions, so no CH₄/N₂O split is available and no AR6 restatement is possible from the published data. The AR5 basis is preserved exactly as published rather than silently rebased — rebasing an aggregate CO₂e figure without the gas mix would be a fabrication.

Geography. These are UK-average factors reflecting the UK supply mix. They are appropriate for fuel purchased in the UK. For fuel purchased elsewhere the upstream mix — particularly the flaring and fugitive-methane profile of the producing region — can differ substantially, and a region-specific dataset is preferable where one exists.

Vintage. DEFRA/DESNZ publish annually in June. Factors change year to year as the supply mix and the underlying evidence base change, so a multi-year time series should apply the factor edition contemporaneous with each reporting year rather than restating history on the newest edition — unless you are deliberately recalculating a base year, in which case say so.

Uncertainty. Upstream factors carry materially wider uncertainty than combustion factors. Combustion is close to stoichiometry and well constrained; upstream depends on modelled estimates of fugitive methane, flaring rates and transport distances that are themselves uncertain and vary by source region. Treat WTT as the less precise half of a well-to-wheel figure.

Implementation & provenance chain

Every row on this page traces to a named cell in the published DEFRA workbook. Nothing is hand-transcribed: the tables above are generated directly from the same MasterBrain rows the REST endpoint serves, and the generator asserts that all 164 source keys render exactly once before the page is built.

Data access — REST API & CSV

The full 164-row dataset is available as a machine-readable REST endpoint and as a flat CSV download. Both serve exactly the rows shown in the tables above, versioned by MasterBrain edition and citable.

Citation guidance

If you use this dataset in a published tool, report or academic work, cite the DEFRA primary source. The GreenCalculus compilation reference is optional but appreciated.

Department for Energy Security and Net Zero (2026). UK Government GHG Conversion Factors for Company Reporting 2026 — well-to-tank factors. London: DESNZ. Contains public sector information licensed under the Open Government Licence v3.0.

DEFRA/DESNZ primary citation

Cite this dataset (GreenCalculus compilation). A versioned, machine-readable snapshot of these factors is archived on Zenodo with a citable DOI:

Say, Jeremiah (2026). UK DEFRA well-to-tank (WTT) upstream fuel emission factors 2026 (machine-readable) (v2026.107). GreenCalculus. Zenodo. https://doi.org/10.5281/zenodo.21831008

GreenCalculus dataset DOI

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