What Is an Emission Factor — and Why Source + Version Decide Whether Your Report Passes
Every carbon figure comes from one equation: activity data × emission factor — and the second half of that equation is where most reports get rejected.
An Emission Factor (EF) is the multiplier that converts activity data — litres of fuel, kWh of electricity, kilometres of freight — into greenhouse gas quantities. Every number in a carbon report comes from the equation "activity data × EF".
EF is not a universal constant
Thailand's grid EF differs from the UK's. TGO's factors are updated in cycles, and old and new values can differ by several percent. Reports that quote an EF without stating its source (TGO / DEFRA / IPCC) and version are among the first to be rejected by verifiers.
Data tiers — from averages to your own measurements
Tier 1 is a standard factor from a central database; Tier 2 adjusts for country or industry context; Tier 3 is measured from your own processes. The higher the tier, the more accurate the report and the more verifiers trust it — organizations with unique processes should develop their own Custom EF.
In GCarbon
The built-in EF library draws from TGO / DEFRA / IPCC with source and version attached to every value. The system filters appropriate EFs per activity type and Scope, supports Custom EF at Tier 2/3, and when a factor set updates it can recalculate historical data while keeping the full history of previous values.
“An EF without source and version is a receipt without a date — unusable as a reference”
Handling a mid-year EF update
When TGO or DEFRA publishes a new set mid-cycle, two approaches are legitimate: keep the old set for the whole cycle for consistency and switch with the new one, or switch mid-cycle with a full historical recalculation. What is wrong is mixing two sets in one cycle. A system that binds every entry to an EF version makes either path a one-click decision.
When a Custom EF is worth the investment
If your process differs materially from the industry average — a proprietary fuel blend, a custom-designed treatment system — Tier 1 values will bias the whole report systematically. Measuring once to build a Tier 3 Custom EF is a one-time cost that lifts accuracy everywhere, and usually pays for itself when that source dominates Scope 1.
GCarbon Team
Carbon accounting specialists
