Emission factors explained: what they are, where they come from and which to use

What is an emission factor?

An emission factor converts an activity into greenhouse gas emissions: emissions equal the activity data multiplied by the emission factor. Activity data is what you measured, such as kilowatt-hours of gas, litres of diesel, kilometres travelled or euros spent. The factor says how much CO₂ equivalent (CO₂e) one unit of that activity releases, in kilograms of CO₂e per kWh, per litre, per kilometre or per euro. For example, 50,000 kWh of natural gas at 0.182 kg CO₂e per kWh gives 9,100 kg, or 9.1 tonnes of CO₂e.

What is inside a factor

Three choices are built into every factor, and they explain most of the differences you will see between datasets:

• The gases: a factor in CO₂e combines carbon dioxide, methane and nitrous oxide, weighted by their global warming potential from an IPCC assessment report. Check which report the publisher used.
• The boundary: a combustion factor covers what leaves your boiler or exhaust, which is Scope 1. The upstream part, from extracting, processing and transporting the fuel, belongs in Scope 3 category 3, fuel- and energy-related activities. Some published factors include both.
• The energy basis: natural gas can be measured on its gross calorific value, which counts the heat in the water vapour, or its net calorific value, which does not. Gas bills in Europe usually state kWh on the gross basis, and a net factor applied to those kWh overstates emissions by about 11%.

The same fuel in three national datasets

For fuels, national datasets agree closely once you compare like with like. For natural gas on the gross basis, the combustion factor is 0.182 kg CO₂e per kWh in the UK government’s 2026 factors, 0.183 in the German Umweltbundesamt’s list and 0.181 in ADEME’s Base Carbone: within about 1% of each other. The gaps that matter come from mixing up the gross and net basis, about 11%, or from including the upstream part or not, 17% to 19%. The table further down shows the three side by side.

Electricity differs by country

Electricity is different: the factor depends on how each country generates its power, and the range is wide. The Joint Research Centre of the European Commission puts electricity generation in 2024 at 0.031 kg CO₂e per kWh in France and 0.511 in Poland, so the same 100,000 kWh is 3.1 tonnes of CO₂e in France and 51.1 tonnes in Poland. For location-based Scope 2, use the factor of the country where the electricity is consumed. For market-based Scope 2, use the factor from your supplier contract or certificates, or the residual mix where you have neither. The table further down lists nine countries.

Where factors come from

Most companies in Europe draw on a handful of public datasets:

• National government sets: the UK government’s greenhouse gas conversion factors from DESNZ, updated every June; the Umweltbundesamt’s list of emission factors for organisations in Germany; and ADEME’s Base Carbone in France, published on its Base Empreinte website.
• Electricity grids: the JRC factors for national electricity generation in Europe, and Ember’s yearly electricity data for most countries in the world.
• Spending: environmentally extended input-output models give factors per euro spent, by sector and country, such as Open CEDA by Watershed and models built on Eurostat’s FIGARO tables.
• Specialised sets: AGRIBALYSE from ADEME and INRAE for food, and Boavizta for IT equipment.
• Your suppliers: a supplier’s own product footprint, or the emission factor in your electricity contract, is more specific than any average.

Choosing the right factor

The GHG Protocol asks for factors that fit the activity and are documented. In practice:

• Match the unit and basis of your data: kWh gross or net, litres or kilograms, kilometres or passenger-kilometres.
• Match the country, above all for electricity and district heating.
• Match the year: use the edition for your reporting year, or the latest available, and say which.
• Prefer the most specific data: supplier-specific first, then activity-based factors, and spend-based factors only where you have nothing better.
• Use one dataset and edition consistently through the year, and record the source, edition and version beside every line.
• When a new edition corrects a factor you used, recalculate your base year if the change is significant. Companies set their own threshold; 5% of the total is common.

Spend-based factors

When you only know what you spent, a spend-based factor estimates the emissions per euro for the sector you bought from, such as office furniture or road freight. It is a good way to screen Scope 3 and find your largest categories, but it reflects average prices and average production. Convert your spending to the factor’s currency and price year, and over time replace spend-based estimates with activity data or supplier data for your largest purchases.

Common mistakes

These errors distort a footprint more than the choice between two good datasets:

• Applying a net factor to gas billed in gross kWh, or the other way round.
• Using another country’s electricity factor, or a factor for another year without saying so.
• Counting upstream emissions twice: inside a total factor in Scope 1 and again in Scope 3 category 3.
• Forgetting to divide kilograms by 1,000 to get tonnes, or mixing up kWh and MWh.
• Switching datasets between years without recalculating the base year, so the trend shows a change of method rather than of emissions.

Doing it in Greener Ahead

Carbon accounting in Greener Ahead selects the factor for each line from the datasets it uses, such as DESNZ, the Umweltbundesamt list and ADEME Base Carbone for fuels, the JRC and Ember for electricity, and Open CEDA for spending, and shows the factor, its source and edition on every line. When a newer edition of a factor you used is published, it asks you to update or keep it, with a reason, before you approve the year. It costs €1,495 per year with unlimited users, and you can try it free for 14 days without a card. Check the pricing page for current details.

Natural gas in three national datasets

Factors for natural gas per kWh on the gross calorific value, the basis used on most gas bills.

Electricity by country

Location-based factors for electricity generation in 2024, from the JRC’s 2026 edition. The UK government’s 2026 factor for UK electricity generated is 0.131.

Check every factor

Before you multiply, check that:

• The unit matches your data.
• The gross or net basis matches your bill.
• Combustion (Scope 1) and upstream (Scope 3) stay apart.
• Electricity and heat use the country where they are consumed.
• The source, edition and year are recorded.