Emission Factor Databases Compared: DESNZ, EPA, IPCC, IEA, ecoinvent

Every emissions figure is activity data times an emission factor. The activity data is yours; the factor almost always comes from someone else. Which database you take it from, and which edition, can move a result by several percent for a fuel and by several times for electricity. This guide lists the main sources as of October 2026 and how to choose between them.

The main databases

Same diesel, three databases

The spread is about 5%. None of the three is wrong: each describes the fuel sold in its market. The error is using one country's factor for fuel bought in another, or mixing editions inside one year's inventory.

Electricity is where the choice matters most

The same consumption gives five times the emissions in India as in the UK. For a company with sites in several countries, using one global average would misstate every site. Use the national factor for each site, and the subregion (eGRID) or state factor where one is official.

How to choose

1. Supplier-specific first. A verified factor from your own supplier (a fuel analysis, a utility's disclosed mix, a supplier's product footprint) beats any database.
2. Then the official national source for the country and year of the activity: DESNZ in the UK, EPA and eGRID in the US, the national grid authority for electricity elsewhere.
3. Then IPCC defaults where no national set exists. They are global and free, and they are what many national inventories use.
4. Licensed databases (IEA, ecoinvent) for what free sets do not cover, such as life-cycle data for purchased materials, checking the licence terms before you publish.
5. Spend-based factors last, for Scope 3 categories where no activity data exists. See spend-based vs activity-based accounting.

Editions: the rule that saves an audit

Most databases publish once a year, and the numbers change, sometimes sharply: the UK grid factor fell by about a quarter between the 2025 and 2026 editions. Apply the edition for the period the activity happened in, keep earlier periods on their own edition, and record the edition next to each figure. Why factors must be versioned and fail closed covers the reasoning; the UK and India grid pages show the editions side by side.

Checklist

• For each activity, record the database, the edition, the row or code, the unit and the global warming potentials used.
• Match the factor's country and year to the activity's, not to your head office or reporting date.
• Keep Scope 2 generation factors separate from T&D losses and well-to-tank factors.
• Report location-based Scope 2 from grid factors, and market-based from contracts or residual mixes.
• Check the licence before publishing results built on paid data.

ZeroCarbon's calculation engine holds a library of published factors with their source and edition, picks the edition by each record's activity date, and refuses to calculate when no factor covers the country instead of falling back to another country's number. You can see this in the free calculator and the emissions API, which return the factor, its source and the formula with every result, or request a workspace to apply it to your own bills.