Emission Factors

In carbon footprint measurement, an emission factor is the coefficient that converts an activity datum (a kWh of electricity, a litre of diesel, a kilometre travelled, a tonne of material) into the corresponding quantity of greenhouse gases (GHGs) emitted. In other words, it indicates how much a given activity contributes to climate change per unit consumed or produced.

What is an emission factor and how is it expressed?

An emission factor is defined as the amount of GHGs released per unit of activity, product or service. The activity unit can be any relevant measure for the case: kilometres travelled, kilowatt-hours consumed, tonnes produced, etc. The result is typically expressed as a mass of CO2 equivalent (CO2e) per unit of activity, for example kgCO2e/kWh or kgCO2e/litre.

The basic calculation is: emissions = activity data × emission factor. For example, for grid electricity in Spain without guarantees of origin, MITECO published a generic factor of 0.283 kgCO2e/kWh for 2024 (compared to 0.260 the previous year); multiplying the annual electricity consumption in kWh by that factor yields an estimate of the associated emissions.

Types of emission factors

By GHG Protocol scope

Factors are classified according to the scope of emissions they represent, following the GHG Protocol:

• Scope 1 (direct emissions): combustion from owned or controlled sources, such as company boilers or vehicles.
• Scope 2 (purchased energy): emissions associated with the electricity, heat or steam that the company purchases and consumes.
• Scope 3 (other indirect emissions): the rest of the value chain (purchases, transport, use of sold products, waste management, etc.).

Location-based and market-based factors (Scope 2)

For Scope 2, the GHG Protocol distinguishes two approaches. The location-based method uses the average emission factor for the local electricity grid (the national or regional mix). The market-based method uses the factor of the electricity product actually contracted, which may be significantly lower or even zero if the electricity comes from renewable sources with guarantees of origin. Good accounting practice typically reports both.

By level of detail

• Generic or default factors: regional, national or global average values, useful for preliminary estimates.
• Specific factors: based on actual data from the facility or supplier, providing a more accurate calculation.

What emission factors are used for

They are the piece that makes it possible to quantify the carbon footprint. They enable:

• Quantifying GHG emissions from each activity and building the emissions inventory.
• Identifying the main hotspots and prioritising reduction measures.
• Setting reduction targets and calculating carbon intensity per unit of product or revenue.
• Monitoring progress consistently over time.

Official sources of emission factors

The reliability of the calculation depends on using factors from recognised and up-to-date sources:

• IPCC: guidelines and default factors for national inventories, along with the global warming potential (GWP) values that convert each gas to CO2e.
• DEFRA / DESNZ (United Kingdom): the UK Government's annual conversion factors, widely used for Scope 3, now published by the Department for Energy Security and Net Zero (DESNZ).
• MITECO (Spain): through the Spanish Climate Change Office, it publishes official electricity and fuel factors each year; these are the reference for calculations in Spain.
• IEA (International Energy Agency): electricity mix factors for numerous countries, useful for international operations.

As a general principle, it is advisable to apply the most specific and up-to-date factor available for each source, always document its origin and year, and maintain the same methodological approach over time so that comparisons remain valid. At Manglai we help companies calculate their carbon footprint using updated emission factors and prepare their sustainability information. Discover how Manglai can help you.