How this calculator works
Food is the largest part of most household footprints after transport and housing, and animal products dominate food emissions. The comparison here is between a vegan diet and the average diet in a high-income country. Scarborough and colleagues compared the diets of more than 55,000 people in the United Kingdom and found that the vegan group produced about 2.47 kg CO2e for every 2,000 calories, against about 4.2 kg for the average diet, a difference of roughly 600 kg of CO2e a year. They also found lower land use and water demand. Multiplying those annual differences by the years you have followed the diet gives a cumulative figure. The estimate assumes your diet before the change matched the national average, which is unlikely to be exact, and it does not count changes in food waste, packaging or air travel, so it shows the scale of the change rather than a precise personal total.
Formula
CO2e avoided = years x 600 kg. land avoided = years x 1,100 m2. blue water avoided = years x 900,000 L. grain avoided = years x grain not fed to livestock per year. animals spared = years x land animals per year. The per-year figures are rounded differences between a vegan diet and the average diet, not values for an individual.
Worked example
Five years vegan. CO2e avoided is 5 x 600 = 3,000 kg, or 3 tonnes. Land is 5 x 1,100 = 5,500 m2, a little over half a hectare. Water is 5 x 900,000 = 4.5 million litres. At 25 animals and 300 kg of grain a year, the totals are 125 animals and 1,500 kg of grain.
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Frequently asked questions
Why is the carbon figure not larger?
It compares a vegan diet with the average diet, not with a very meat-heavy one. Someone who ate beef most days can save considerably more, while someone who was already vegetarian saves less. The annual difference is the honest comparison.
Is a vegan diet always lower impact?
On land, water and greenhouse gases, the evidence is consistent across large studies. Individual foods matter: air-freighted produce, out-of-season greenhouse vegetables and highly processed substitutes can raise the footprint. The average still comes out lower.
How is the animal count calculated?
It is a dietary average, not a count of every creature. A person eating a typical high-income diet consumes several dozen farmed fish, around 25 to 30 land animals, mostly chickens, and a fraction of a cow or pig each year. The input lets you adjust it.
Does the grain figure really matter?
It captures the feed that would have been grown for livestock. Growing feed uses land, water and fertiliser, so reducing it is part of the land saving already counted. The grain figure is there to make the feed conversion visible, not as a separate claim.
Sources
- Scarborough et al. (2023), Vegans, vegetarians and fish-eaters in the UK have lower dietary greenhouse gas emissions, Nature Food
- Mekonnen and Hoekstra (2012): a global assessment of the water footprint of farm animal products, Ecosystems
- Food and Agriculture Organization: livestock and the food chain, feed conversion and cereal use
- Environment and Climate Change Canada: emission factors and reference values for greenhouse gas quantification (national inventory edition, updated annually)