Where do the emission factors come from?

They are derived from the 2018 Poore and Nemecek meta-analysis in Science, the largest food lifecycle study to date, covering production, processing, transport, and retail. Figures are expressed per kilogram and converted here to a typical serving size for each category.

Why is beef so much higher than chicken or beans?

Ruminant animals like cattle and sheep emit methane through digestion and need large amounts of land and feed. Beef averages around 60 kg CO2e per kilogram, lamb about 24, while poultry is near 6 and most legumes and vegetables under 2. That is why red meat dominates most meat-eaters' diets.

Are serving sizes standardised?

Each category uses a sensible default serving — for example 100 g for cooked meat, 200 ml for milk, one egg, 80 g for a portion of vegetables. These are planning estimates, so treat the totals as indicative rather than precise to the gram.

How does my diet compare to average?

A typical high-meat Western diet produces roughly 2,500 kg CO2e per year from food, an average diet around 1,700, a low-meat diet near 1,200, and a fully plant-based diet often under 1,000. The biggest single lever is reducing beef and lamb.

Does this include food waste or cooking energy?

No. The factors cover food production through retail, not the energy you use cooking at home or food thrown away. Both add to a real footprint, so the figure shown is a conservative lower bound for the food itself.

Diet & Food Carbon Footprint Calculator

What you eat is one of the largest parts of a personal carbon footprint, and the difference between food types is enormous — a kilogram of beef can carry thirty times the emissions of a kilogram of beans. This calculator turns your weekly eating habits into an annual CO2e figure using peer-reviewed lifecycle data.

How it works

For each food category the calculation is simple and transparent:

category annual CO2e = weekly servings × serving size (kg)
                       × emission factor (kg CO2e per kg)
                       × 52 weeks
total = sum of all categories

Emission factors come from the Poore and Nemecek lifecycle dataset, the most comprehensive available, and each is paired with a realistic serving size so a serving of steak and a serving of lentils are compared fairly.

Example and tips

Eating beef four times a week alone contributes roughly 1,250 kg CO2e a year — often more than every other food category combined for a typical eater. Swapping half of those beef meals for poultry cuts that to about 750, and swapping them for legumes drops it under 100. The highest-leverage changes are almost always reducing beef and lamb first; dairy is the next largest lever, while vegetables, grains, and legumes barely move the total.