Glossary›Emissions accounting and measurement›Emission factor
Glossary term
Cluster D · D12
Tier 1
Emission factor
Definition
An emission factor is the published coefficient that converts a quantity of activity data into a quantity of greenhouse gas emissions, expressed in carbon dioxide equivalent. Multiplying litres of diesel by a diesel factor gives tonnes of CO2-e. Factors are revised periodically, so the factor set and the edition applied are part of the reported number rather than a footnote to it.
AASB S2 Appendix B
· paragraphs B22, B26 and B29 ·
In force
On this page
In practice
AASB S2 does not tell you which factors to use, and reporters routinely expect that it does. Appendix B paragraph B29 states the position plainly: the standard does not specify emission factors an entity is required to use, and instead requires the entity to use emission factors that best represent the entity’s activity. Paragraph B22 says the same thing from the other side, requiring the entity to use, as its basis for measurement, the factors that best represent its activity.
That places the burden on the reporter. “Best represent the entity’s activity” is a judgement, and it is a disclosed judgement, because paragraph B26 requires an entity to disclose the emission factors it uses as part of its measurement approach.
Three dimensions decide whether a factor selection holds up.
Dimension
What it decides
Geography
Australian grid electricity factors vary substantially between states and territories, and the difference is not cosmetic. Using a national average for a business concentrated in one state misrepresents the activity. A multi-state business needs factors per state, applied to consumption per state.
Specificity
A supplier-specific factor beats a national published average where one exists and is credible. This is the point where the emission factor question meets the primary versus secondary data question, and the two are answered together.
Edition
Factors change annually. A figure calculated with a 2024 factor and a figure calculated with a 2025 factor are not comparable without adjustment, and a trend built across editions without noting the change is a misleading trend.
There is one Australian carve-out worth holding onto. Paragraph B22 provides that where an entity’s factors have already converted the constituent gases into CO2 equivalent values, the entity is not required to recalculate them using global warming potential values from the latest IPCC assessment. Most published Australian factor sets already arrive in CO2-e, so for most reporters the global warming potential question resolves itself at the factor selection step rather than being a separate calculation.
What the assurer does with it
Factor testing is the cheapest part of the engagement for the assurer and the most frequently failed part for the entity, because it is entirely documentary. There is no judgement to explore and no sample to project. The factor is either the right one, correctly cited and correctly applied, or it is not.
The assurer re-performs. They take the activity quantity, look up the factor in the cited source edition, multiply, and compare to the reported figure. A difference means one of three things: wrong factor, wrong edition, or an undisclosed adjustment in between.
They accept a factor traced to a named published source with a stated edition or year, applied to the correct activity category and the correct jurisdiction. They reject a factor with no cited source, a factor from a superseded edition applied to a current period with no explanation, a factor hardcoded into a model with no lookup and no documentation, and a factor applied to an activity category it was not published for: a heavy vehicle factor applied to a passenger fleet, for example.
The follow-up question where a supplier-specific factor is used is provenance: how was the supplier’s factor calculated, and has it been verified by anyone. A supplier-specific factor the supplier cannot substantiate is weaker evidence than a published national average, even though it looks more precise.
Commonly confused with
Global warming potential, which is a different conversion. A global warming potential converts one gas into CO2-e; an emission factor converts an activity into emissions. A factor may have a global warming potential already baked into it, which is why the two get run together.
Sources
1
2
3
Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard (2004 revised edition)
GHG Protocol
Review status
Review required
Last reviewed
15 September 2026
Editorial pass, unsigned
Reviewer required
Carbon accounting specialist
Next scheduled review
1 August 2027
next expected National Greenhouse Accounts Factors release
Part of
Cluster D, Emissions accounting and measurement
49 terms from the head term carbon accounting down to individual Scope 3 categories and the mechanics of factors, boundaries and data quality. The largest cluster in the glossary.
Related terms
The physical quantity the factor is applied to
The default Australian factor set and its annual edition cycle
The separate conversion most Australian factor sets have already applied
Related questions
Where do Australian emission factors come from?
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The National Greenhouse Accounts Factors, published each year by the Department of Climate Change, Energy, the Environment and Water. They give Scope 1 factors by fuel and Scope 2 electricity factors by state and territory. NGER-registered corporations must use NGER measurement methods for their NGER reporting.
We have sites in several states. Does that change our emission factors?
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Yes, for electricity. Location-based Scope 2 factors differ by state and territory because grid intensity differs, so you need electricity consumption split by site and state and then the matching factor for each. Scope 1 fuel factors are national and do not change from one state to another.
What evidence do we need for each emissions number?
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Every reported number needs a source document you did not create for the report, the activity data drawn from it, the emission factor and its published edition, and the calculation joining them. Fleet fuel needs litres from fuel card statements, electricity needs kWh by site from retailer invoices with the matching state factor, and refrigerants need kilograms by gas type from service records.
Other terms in this cluster
Emission factor