How BlocCarbon calculates carbon footprints
By the BlocCarbon methodology team · Published 3 August 2026 · Last updated 3 August 2026
Every number BlocCarbon shows is the product of an official, versioned emission factor and a quantity you entered — computed on our servers, never estimated in your browser. This page lists every source we use, the formulas we apply, and the rules that keep results reproducible.
Which sources do we use?
Only official government-published or peer-reviewed factor sources. We never invent factors, and every calculation line is labelled with the source that produced it.
| Source | Publisher | Used for | Licence |
|---|---|---|---|
| Greenhouse-gas conversion factors 2026 (flat file, revised 31 July 2026) | UK Department for Energy Security and Net Zero (DESNZ) | Energy, road/rail/air/sea passenger transport, freight, hotels, materials, waste, homeworking | Open Government Licence v3.0 |
| Agribalyse 3.1 | ADEME / INRAE (French government) | Food items (~2,500 ready-to-eat foods) | Open licence (data.gouv.fr) |
| The Big Climate Database 1.2 | CONCITO (Denmark) | Food items (~500 foods, English) | Free to use |
| Scarborough et al. 2014, 'Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK' (Climatic Change) | Peer-reviewed (University of Oxford) | Per-day diet-pattern factors in the food calculator | Published research |
| OurAirports | Community, public domain | Airport locations (~9,000 IATA-coded) for flight distances | Public domain |
How are factor sets versioned?
DESNZ republishes its conversion factors every June, often with a mid-summer revision — the 2026 flat file we use was revised on 31 July 2026. Each release is ingested as a new, immutable factor set; one set per source is active at a time. Every submission stores the id of the factor set and the individual factor behind each line, so a result computed today can be audited years later against exactly the data that produced it. Published calculators are versioned the same way: campaigns pin a calculator version and never drift.
How are flights calculated?
Distance is the great-circle distance between the two airports (haversine formula, Earth radius 6371.0088 km) plus the 8% uplift DEFRA prescribes for real-world routing and holding patterns. The corrected distance determines the haul class (domestic, short-haul or long-haul), and the DESNZ 2026 factor for that haul and cabin is applied per passenger-km. We use the with-radiative-forcing variants by default — the government-recommended treatment of aviation's altitude effects, a ×1.7 multiplier in the 2026 set. Example factors: short-haul economy 0.12576, long-haul economy 0.11704 kgCO2e per passenger-km (with RF).
What are the key 2026 factors?
From the DESNZ 2026 flat file (revised 31 July 2026): UK grid electricity 0.13096 kgCO2e/kWh; national rail 0.03092 kgCO2e per passenger-km; average car (unknown fuel) 0.16591 kgCO2e/km; UK hotel stay 10.4 kgCO2e per room-night. Food factors come from Agribalyse and The Big Climate Database and are labelled per line. Browse the full explained set on our emission factor pages.
Where do the benchmarks on results pages come from?
- UK average ≈ 6.2 tonnes CO2e per person per year — ONS UK per-person emissions on a territorial basis, an approximate orientation figure (consumption-based estimates run higher).
- London–New York return ≈ 1,400 kg CO2e — derived from the DESNZ 2026 long-haul economy with-RF factor applied to the great-circle distance + 8%, both directions.
- Car comparison, 0.16591 kgCO2e/km — the DESNZ 2026 average car (unknown fuel) factor.
What do events use, given no official event factor exists?
No government publishes a per-event factor, so our event calculator is a composite of official per-component factors: attendee travel by modal split (DESNZ passenger transport), accommodation (DESNZ per-country room-nights), venue energy (metered kWh × the UK grid factor), catering (per-meal figures derived from The Big Climate Database and Agribalyse typical portions, labelled as derived), materials (DESNZ material-use factors) and waste (DESNZ waste-disposal factors). The total divides by attendee count for a per-attendee figure.
What claims does funding support?
Funding verified climate projects through BlocCarbon is a contribution to climate action — we state it exactly that way: “funded X tCO2e of verified climate projects”. We do not generate “carbon neutral” badges or equivalence claims, in line with the EU Empowering Consumers for the Green Transition Directive and the UK CMA Green Claims Code. Certificates state what was measured and what was funded, nothing more.
Limitations
- Factors are national averages: your specific car, home or hotel will differ from the fleet or stock average.
- Food databases differ in system boundaries; we label each line's database rather than blending sources into one number.
- We deliberately exclude categories with no defensible official source — for example digital/streaming, where published estimates disagree by an order of magnitude.