Glossary›Emissions accounting and measurement›Emissions measurement vs estimation
Glossary term
Cluster D · D27
Tier 1 · differentiator
Emissions measurement vs estimation
Definition
Measurement derives an emissions figure from a recorded physical quantity, such as metered electricity or invoiced fuel volume. Estimation derives it from a proxy, an average or a model where the actual quantity is unavailable. Both are permitted in a compliant inventory. The difference is the strength of the evidence behind the number and the disclosure required about it.
GHG Protocol Corporate Standard (2004)
· chapter 6 and the data quality provisions ·
In force
On this page
In practice
The distinction is treated as a quality gradient when it is really an evidence category. A measured figure rests on a record created by an outside party at the time of the activity. An estimated figure rests on a method and a set of assumptions created by the entity. The assurer tests those two things in completely different ways, and an entity that does not label which is which forces the assurer to guess.
Pure measurement is rarer than reporters expect.
Figure
Which side of the line
Metered electricity on an invoice
Measured
Fuel purchased on a card statement in litres
Measured
Fuel expense in dollars converted to litres at an assumed price
Estimated, even though it started life as a real invoice, because an assumption entered the calculation
Floor-area-apportioned landlord electricity
Estimated
Spend-based Scope 3
Estimated throughout
The practical rule is that a figure is estimated the moment a number the entity chose enters the chain. That moment is where the documentation obligation starts.
What the assurer does with it
For a measured figure, the assurer vouches to the source document and agrees quantity, period and entity. For an estimated figure, that route does not exist, so they test the method instead. They ask for the method statement, the inputs and their sources, the calculation, and who approved it. They then re-perform it, and often substitute an alternative input to see how far the answer moves.
They accept an estimate where the method is documented, applied consistently across comparable sources, based on inputs with a traceable origin, and accompanied by a statement of what it could not capture. They reject an estimate with no written method, an estimate whose inputs cannot be sourced, and an estimate whose basis changed between periods with no disclosure: the last one because it makes the trend meaningless.
The question that ends the conversation badly is the sensitivity one: if this assumption were wrong by a plausible margin, would the disclosed figure move by more than materiality. If the answer is yes and there is no documented basis for the assumption, the assurer will press for better data rather than accept a range.
ASSA 5000 addresses estimates specifically rather than leaving them to the general evidence obligation. Paragraph 146R governs the practitioner’s work on estimates, and application paragraph A460R describes developing a point estimate or range to evaluate estimates and related disclosures, appropriate for example where the practitioner’s review of similar prior-period estimates suggests management’s current process is not expected to be effective. In practice that means a modelled emissions figure can be met with the assurer’s own independently developed range.
Commonly confused with
Primary versus secondary data, which is a different axis. Primary data can be estimated (a supplier’s own modelled figure) and secondary data can be measured (a published metered average). Measurement versus estimation describes how the number was derived; primary versus secondary describes who derived it.
Sources
1
Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard (2004 revised edition)
GHG Protocol
2
ASSA 5000 General Requirements for Sustainability Assurance Engagements
AUASB
3
Review status
Review required
Last reviewed
15 September 2026
Editorial pass, unsigned
Reviewer required
Carbon accounting specialist and registered company auditor
Next scheduled review
1 July 2027
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 process both evidence categories sit inside
How to build and defend the estimate once you are on that side of the line
The four characteristics that rank the evidence behind each line
Related questions
Can we estimate Scope 3 and still pass assurance?
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Yes. Estimates are expected in Scope 3 and are not a problem for assurance in themselves, because what fails is an undocumented estimate. The practitioner tests whether the method is appropriate and disclosed, the inputs are traceable, the application is consistent, and the estimation uncertainty is described honestly.
What evidence do we need for each emissions number?
+
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.
Can we use spreadsheets, or will the auditor reject them?
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Spreadsheets are acceptable and no Australian standard requires software. What gets rejected is an unauditable spreadsheet: hard-coded numbers with no source, broken formula chains, no version control and no record of who changed what. A disciplined spreadsheet passes assurance and an undisciplined system does not.
Where this sits commercially
Carbonhalo labels every line measured or estimated in the inventory itself, so the assurer does not have to guess which procedures apply.
Other terms in this cluster
Emissions measurement vs estimation