Emission Factor
An emission factor is a coefficient that converts a unit of activity — such as one kilowatt-hour of electricity consumed, one litre of fuel burned, or one pound spent on a purchased service — into the corresponding quantity of greenhouse gas emissions, expressed in kgCO₂e.
What is Emission Factor?
Emission factors are the conversion ratios at the heart of carbon accounting. They bridge the gap between what an organisation can easily measure (activity data — energy bills, fuel receipts, travel bookings, procurement spend) and what it needs to report (greenhouse gas emissions in tCO₂e). Without emission factors, there is no way to translate business operations into a carbon footprint.
An emission factor typically represents the mass of greenhouse gas emitted per unit of activity. For example, the DEFRA 2024 emission factor for UK grid electricity is approximately 0.207 kgCO₂e per kWh, meaning every kilowatt-hour of electricity consumed generates about 207 grams of CO₂e at the national grid average. For diesel, the factor is approximately 2.51 kgCO₂e per litre. For natural gas, approximately 0.183 kgCO₂e per kWh.
Emission factors are published by a range of sources at different levels of specificity. Government-published factors, such as the UK's DEFRA/DESNZ dataset, provide nationally representative averages and are the standard for regulatory reporting. International databases include the IEA (country-specific electricity grid factors), the US EPA (for US operations), and ecoinvent (lifecycle assessment factors). For Scope 3 spend-based calculations, environmentally extended input-output (EEIO) factors — such as those from DEFRA, the US EPA Supply Chain Factors, or Exiobase — express emissions per unit of economic activity (e.g., kgCO₂e per £ spent).
The accuracy of a carbon footprint depends heavily on the choice of emission factor. A hierarchy of data quality applies: supplier-specific emission data is the most accurate, followed by activity-based factors (e.g., kgCO₂e per kWh), then average-data factors (e.g., kgCO₂e per tonne of material), and finally spend-based factors (e.g., kgCO₂e per £). Organisations should use the most specific factor available and work to improve data quality over time.
Emission factors change annually as energy grids decarbonise, fuel supply chains evolve, and GWP values are updated. Using the correct year's factor for the corresponding reporting period is essential for accuracy and comparability.
Practical Examples
A facilities manager multiplies 800,000 kWh of natural gas consumption by the DEFRA natural gas emission factor (0.183 kgCO₂e/kWh) to calculate 146.4 tCO₂e of Scope 1 emissions from heating.
A procurement team uses DEFRA spend-based emission factors to estimate Scope 3 Category 1 emissions: £2 million spent on IT equipment at 0.21 kgCO₂e per £ yields approximately 420 tCO₂e.
An international company uses the IEA grid emission factor for Germany (0.385 kgCO₂e/kWh) for its Berlin office and the DEFRA UK grid factor (0.207 kgCO₂e/kWh) for its London office, reflecting the different carbon intensities of each country's electricity supply.
How Climatise Helps
Climatise maintains a library of over 50,000 emission factors — including every DEFRA/DESNZ factor, IEA grid factors, and EEIO spend-based factors — updated annually. The platform automatically matches your activity data to the correct factor based on type, unit, country, and reporting year.
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