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Definition

GHG allocation key

A greenhouse gas (GHG) allocation key is a measurable driver used to divide shared emissions among products, services, sites, contracts, or customers when emissions cannot be measured separately for each output.

What is a GHG allocation key?

A GHG allocation key splits one facility or system emissions total among its outputs. Chapter 8 of the GHG Protocol Scope 3 Standard names mass, volume, energy, floor area, units produced, and market value as possible drivers.

Why does a GHG allocation key matter to you?

A customer may ask for emissions attached to its products when one meter covers the factory. Your method note should identify the shared total, period, outputs, driver, units, and calculation. Allocated shares must add to 100%, or emissions are omitted or counted twice.

How does a GHG allocation key work?

Use direct product data or sub-metering first. Otherwise divide each output's driver by the total driver, then multiply by shared emissions. Suppose a furniture maker in Spain records 12 tonnes of carbon dioxide equivalent (tCO2e) for one finishing line. Tables use 480 of 1,200 machine hours, so they receive 40%, or 4.8 tCO2e. Chairs use the remaining 720 hours, so they receive 60%, or 7.2 tCO2e.

What mistakes should you avoid?

  • Using revenue when machine hours or another physical driver better explains energy use.
  • Mixing kilograms, tonnes, hours, or units between the numerator and denominator.
  • Allocating only the requested customer's share without checking that all outputs total 100%.
  • Changing the key between reporting periods without recording the reason and effect.

Which allocation key should you choose?

Choose the physical measure that best tracks the emissions source. Machine hours may suit powered finishing; floor area may suit shared storage. Use economic value only when no physical relationship can be established, and record the prices and period.

What records should you keep for an allocation?

Keep the source total, calculation file, output list, driver records, numerator, denominator, percentage, allocated tCO2e, reporting period, method approval, and a reconciliation to the original total.

Where it comes up

GHG Protocol Scope 3 allocation method and single-factor reconciliationCorporate Value Chain (Scope 3) Standard, Chapter 8, sections 8.1-8.3, pages 88-91Official sourceGHG Protocol Scope 3 disclosure of allocation methods and assumptionsCorporate Value Chain (Scope 3) Standard, Chapter 11, section 11.1, pages 120-122Official sourceGHG Protocol Product Standard allocation hierarchy and factor choiceProduct Life Cycle Accounting and Reporting Standard, Chapter 9, sections 9.2-9.3.3, pages 63-70Official source

Related terms

Product carbon footprint (PCF)

A product carbon footprint (PCF) is the greenhouse gas emissions assigned to one product across a stated life-cycle boundary and expressed per declared or functional unit.

Scope 3 Emissions

Scope 3 emissions are the indirect greenhouse gas emissions from goods, services, transport, product use, investments, and other upstream and downstream activities outside your company's Scope 1 and Scope 2 boundary.

Primary vs secondary GHG data

Primary GHG data records a specific site, product, activity, or supplier, while secondary GHG data estimates that activity with external averages, databases, financial factors, or other proxies.

GHG accounting principles

GHG accounting principles require an inventory to be relevant, complete, consistent, transparent, and accurate so its boundary, methods, exclusions, and results can support decisions and withstand review.

Functional unit (LCA)

A functional unit states the quantified performance a product or service must deliver, giving an LCA one reference against which every input, output, and environmental result is measured.

Sources

  • GHG Protocol

    Chapter 8 allocation need, method selection, single-factor use, 100% reconciliation, and Chapter 11 disclosure

    2026-08-20

  • GHG Protocol

    Chapter 9 allocation hierarchy, physical and economic factors, consistency, and documentation

    2026-08-20

Last verified 2026-08-20

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GHG allocation key Definition | Keslio