How the
engine works.
Every number the platform produces comes from a published emission factor with a version, a source and an activity unit attached. This page sets out where the factors come from, which standards we follow, and a fully worked example so you can check the arithmetic yourself.
Data sources
The engine draws on four factor libraries, applied in this order of preference:
- UK DESNZ/BEIS 2024 emission factors (published by the Department for Energy Security and Net Zero, successor to BEIS) for UK fuel, electricity and travel activity.
- DEFRA conversion factors for food, waste and water categories.
- IPCC AR6 global warming potentials, used to convert other gases to CO2e over a 100-year horizon.
- EC3 (Building Transparency) environmental product declaration data for construction materials such as concrete, steel and timber.
Each factor is stored with its publication year. When a library updates, previous reports keep the factors they were calculated with, so a restated number is always labelled as a restatement rather than silently overwritten.
EN 15978 lifecycle modules
For construction and materials work we map results to the EN 15978 building lifecycle stages: A1 to A3 (product stage, raw material supply, transport and manufacturing), A4 to A5 (construction), B1 to B7 (use, maintenance, repair, energy and water), C1 to C4 (end of life, demolition and disposal) and D (benefits beyond the system boundary, reported separately and never netted off). Materials measured from EC3 EPDs sit in A1 to A3; transport and site works land in A4 and A5.
GHG Protocol scopes
For organisational reporting we follow the GHG Protocol Corporate Standard: Scope 1 for direct emissions from sources you own or control, Scope 2 for purchased electricity, heat and steam on a location basis, and Scope 3 across the value chain using the relevant categories from the Corporate Value Chain standard. Business reports show which categories are estimated, which are measured and which are excluded, and never present a gap as completeness.
Worked example: 100 kg of concrete
Take a stated mix with a product-stage figure of 0.103 kg CO2e per kg from an EC3 EPD. For 100 kg of concrete, the product stage is:
100 kg × 0.103 kg CO2e/kg = 10.3 kg CO2e (A1–A3)
If 30 km of lorry transport is then added at the BEIS rigid HGV factor of about 0.18 kg CO2e per tonne-kilometre, stage A4 contributes 0.1 t × 30 km × 0.18 = 0.54 kg CO2e. The total cradle-to-site figure is 10.84 kg CO2e, and every line of it links back to the factor, its year and its source.
That is the whole trick, done honestly at scale: activity multiplied by a factor you can name, a standard you can check, and an uncertainty we publish rather than hide.
Sources: UK DESNZ/BEIS greenhouse gas reporting conversion factors · DEFRA conversion factors · IPCC Sixth Assessment Report · EC3 / Building Transparency.