What the calculator covers
The calculator estimates your personal annual greenhouse-gas emissions in kilograms of CO₂-equivalent (CO₂e) across four categories:
- Transport (car, public transit, flights)
- Home energy (electricity, heating)
- Food (diet pattern)
- Goods & services (consumption-based residual)
CO₂e is the standard unit for comparing different greenhouse gases. It converts methane, nitrous oxide, and fluorinated gases into the equivalent warming impact of CO₂ over a 100-year window (the GWP-100 metric used by the IPCC).
Where the numbers come from
- Transport and energy factors come from the UK Defra / DESNZ annual GHG conversion factors (2024 edition) — the most widely-cited public dataset for emissions per kWh of grid electricity, per km of various vehicle types, and per passenger-km for flights at short, medium, and long haul. The dataset is updated yearly to reflect grid decarbonization.
- Food factors come from Poore & Nemecek's 2018 meta-analysis in Science — at the time the largest assessment of food-system emissions, covering roughly 38,000 farms across 119 countries and 40 food products. The category-level factors (beef ~60 kg CO₂e/kg, poultry ~6, lentils ~0.9) drive the diet-pattern presets.
- Goods & services uses an input-output average derived from IPCC AR6 WG3 (2022) consumption-side data, scaled to the user's reported region.
A worked example
A user in Germany who:
- Drives 12,000 km/year in a mid-size petrol car (~1.7 t CO₂e)
- Takes one return economy flight Frankfurt → New York (~2.2 t)
- Lives in a 70 m² apartment with the average German electricity mix (~1.0 t)
- Eats a mixed Western diet without much red meat (~1.8 t)
- Adds a residual goods-and-services footprint of ~2.5 t
…lands at roughly 9.2 tonnes CO₂e/year — slightly above the German per-capita average (~7.9 t in 2024) and well above the IPCC-aligned ~2 t/year per person needed by 2050 to stay on a 1.5°C pathway.
What actually moves the number
Wynes & Nicholas (2017) ranked individual mitigation actions by impact. The largest single-action reductions in their analysis: live car-free (~2.4 t/year), avoid one transatlantic return flight (~1.6 t), shift to a plant-based diet (~0.8 t), switch to a renewable-electricity tariff (~1.5 t depending on grid). These dwarf the actions commonly emphasized in public-information campaigns (recycling, hanging laundry, swapping bulbs) by an order of magnitude. The calculator weights its suggestions accordingly.
Limitations
Personal carbon calculators are approximate by nature. National emission factors blur substantial variation: a Norwegian electric car charged on hydro grids and a Polish electric car charged on coal grids carry very different per-km footprints, but a global "EV per km" average obscures both. The diet category likewise averages across cuisines, sourcing, and seasonality — local, in-season vegetables and imported, out-of-season equivalents can differ by an order of magnitude.
The goods-and-services residual is the least precise category. It relies on national average consumption-expenditure data rather than on what you specifically buy. Two people with identical transport, energy, and diet footprints can have legitimately different residual footprints if one buys heavily and the other lives sparely.
Concept-of-responsibility ambiguity is unavoidable. A flight's emissions are split differently under territorial accounting (where the fuel was burned), consumer-based accounting (the passenger's home country), and corporate accounting (the airline's home country). This calculator uses consumer-based attribution, the most common framing for individual footprint estimation.