EPA emission factors: which ones to use for Scope 1, 2 and 3

For a US company, the emission factors to use are the free EPA sources for each scope: the EPA GHG Emission Factors Hub for Scope 1 direct combustion, eGRID for Scope 2 purchased electricity, and the USEEIO environmentally extended input-output model for spend-based Scope 3. These are the libraries most US inventories are built on, they are published and updated by the federal government, and they cost nothing. The skill is not finding exotic factors; it is picking the right public one for each line and documenting which version you used.

An emissions figure is always the same shape: activity data times an emission factor. You measure how much of something happened, a therm of gas burned, a kilowatt-hour bought, a dollar of steel purchased, and multiply by a factor that converts it to carbon dioxide equivalent. Get the activity data from your own records; get the factor from a recognized source. Here is which source, for each scope.

Scope 1: the EPA GHG Emission Factors Hub

For Scope 1, direct emissions from fuel you burn on site, use the EPA GHG Emission Factors Hub. The Hub is a single spreadsheet the EPA updates each year that consolidates the key US factors: stationary combustion (natural gas, diesel, propane), mobile combustion for fleet vehicles, and fugitive emissions such as refrigerant leakage. Roughly 80% of US companies use the Hub for Scope 1, and it is the path-of-least-resistance answer for direct energy. You take the fuel quantity off the invoice, find the matching fuel in the Hub, and multiply.

The Hub also carries factors for common Scope 3 activities the EPA has standardized, business travel, employee commuting, waste disposal and upstream and downstream transport, so it does double duty beyond Scope 1. When someone says they used EPA factors, the Hub is usually what they mean.

Scope 2: eGRID for purchased electricity

For Scope 2, the electricity you buy, the authoritative US source is eGRID, the EPA's Emissions and Generation Resource Integrated Database. eGRID publishes the carbon intensity of the US grid by region, so you convert kilowatt-hours to emissions using the factor for the subregion your facility sits in, rather than a single national average. The annual Hub update pulls the latest eGRID electricity factors through, so the two stay aligned.

eGRID gives you the location-based Scope 2 number, the grid-average method. If you buy renewable energy through contracts or RECs, you also report a market-based number using supplier-specific or residual-mix factors. The GHG Protocol requires both. Our guide to location-based vs market-based Scope 2 explains why you report two figures and which one regulators want.

Scope 3: USEEIO for spend-based estimates

For spend-based Scope 3, the factors come from an environmentally extended input-output model, and the US public option is USEEIO, built by the EPA. An input-output model gives you an emission factor per dollar of spend in a given industry category, kilograms of CO2e per dollar spent on, say, iron and steel or office supplies. You classify each accounts-payable line to a category and multiply the spend by the matching factor. It is coarse, an industry average rather than your specific supplier, but it is complete: it lets you screen an entire AP file and see where the footprint concentrates. USEEIO and the related CEDA model are used by well over half of organizations for Scope 3 screening.

The spend-based method is how most companies get their first Scope 3 number, and our step-by-step guide to calculating Scope 3 from spend walks through it with the factors. The judgment of when a coarse spend estimate is good enough and when to graduate to supplier-specific activity data is covered in spend-based vs activity-based emissions.

Which EPA emission factor source to use, by scope

Scope	Activity	Free US source
Scope 1	Fuel combustion, fleet, refrigerants	EPA GHG Emission Factors Hub
Scope 2	Purchased electricity (location-based)	EPA eGRID
Scope 3	Spend-based screening of purchases	EPA USEEIO input-output factors
Scope 3	Travel, commuting, waste, transport	EPA GHG Emission Factors Hub

Document the factor and its version, every time

The single most important habit is recording which factor you used and which year's version it came from. Factors change: the Hub and eGRID are reissued annually as the grid decarbonizes and methods improve. If your inventory does not say "eGRID 2025, subregion CAMX" against a line, then next year, when the factor updates, nobody can tell whether a change in your number is a real emissions change or just a newer factor. That ambiguity is exactly what an assurance provider will not accept. Versioning the factor per line is not bureaucracy; it is what makes year-over-year comparison and restatement possible at all.

This is easier when the spend data is already clean and queryable. Getting from a raw AP or ERP export to a categorized table you can ask plain-English questions of, which suppliers dominate, which categories carry the spend, is half the battle before a single factor is applied. Our carbon accounting software does that mapping and then attaches the exact factor and version to every figure automatically, so the audit trail is a by-product of the calculation rather than a separate documentation chore.

When to look beyond the EPA sources

The EPA libraries cover the vast majority of a US inventory, but a few cases call for more. Companies with material overseas operations need country-specific grid factors rather than eGRID. Firms with big, well-understood purchased-goods lines eventually replace USEEIO spend factors with supplier-specific or product-level data, such as Environmental Product Declarations, for their largest materials. And some activities, like certain industrial processes, need factors from the EPA's other programs or from primary measurement. The rule of thumb: start with the free EPA sources to get a complete number, then upgrade the specific lines that are big enough to justify the effort. For the wider standard these factors plug into, see the GHG Protocol Corporate Standard, and to put it all together into a first report, the GHG inventory checklist. If your reporting driver is California, SB 253 reporting software covers that regime.