Personal carbon footprint calculator

How to calculate your carbon footprint

Multiply each activity by its emission factor and add the results: liters of fuel × kg CO₂e per liter, passenger-kilometers × a travel factor, your share of home electricity × the grid factor, and a daily diet figure × 365. On UK 2024 factors, the worked example below comes to 4.57 t CO₂e a year.

The total covers driving, flights, rail, bus, home electricity and diet. Gas heating, purchases, services and the manufacture of the car sit outside it, so the result is a partial footprint.

Worked example: one person's year

1. Car: 12,000 km at 7 L/100 km burns 840 L of petrol, and 840 × 2.0844 = 1,750.896 kg.
2. Flights: 2,000 km of short-haul flights × 0.18592 = 371.84 kg.
3. Train and bus: 1,000 km × 0.03546 + 500 km × 0.10846 = 89.69 kg.
4. Electricity: 2,700 kWh shared by 2 people is 1,350 kWh each, and 1,350 × 0.22535 = 304.2225 kg.
5. Diet: medium meat at 5.63 kg a day × 365 = 2,054.95 kg.

The sum is 4,571.6 kg, or 4.57 t CO₂e. Diet is the largest part at 45%, ahead of the car at 38%.

Emission factors used

Transport and electricity factors are the UK government's 2024 greenhouse gas conversion factors from DESNZ, in kg CO₂e:

• Petrol: 2.0844 per liter. Diesel: 2.51279 per liter.
• Flights, per passenger-km: 0.27257 domestic, 0.18592 short-haul (under 3,700 km a flight) and 0.26128 long-haul.
• Rail and bus, per passenger-km: 0.03546 for national rail and 0.10846 for a local bus.
• UK grid electricity: 0.22535 per kWh, the 0.20705 generation factor plus 0.01830 for transmission and distribution losses.

Diet factors come from Scarborough et al. (2014), who analyzed the diets of UK adults in the EPIC-Oxford cohort and scaled them to 2,000 kcal a day:

• High meat (100 g a day or more): 7.19 kg a day, 2,624 kg a year.
• Medium meat (50–99 g a day): 5.63 kg a day, 2,055 kg a year.
• Low meat (under 50 g a day): 4.67 kg a day, 1,705 kg a year.
• Fish but no meat: 3.91 kg a day, 1,427 kg a year.
• Vegetarian: 3.81 kg a day, 1,391 kg a year.
• Vegan: 2.89 kg a day, 1,055 kg a year.

Car and diet changes compared

Each row changes one thing from the worked example. Switching the petrol car for an electric one saves 1,291 kg a year, going vegan saves 1,000 kg, and giving up the car saves the full 1,751 kg.

Diesel at the same 7 L/100 km adds 360 kg, because a liter of diesel carries 20.6% more CO₂e than a liter of petrol.

Petrol, diesel or electric car

Per kilometer, a petrol car at 7 L/100 km emits 146 g CO₂e. An electric car using 17 kWh/100 km on the UK grid emits 38 g; only a grid at 0.86 kg CO₂e per kWh would bring it level with the petrol car.

A diesel car emits less than a petrol one only if it burns more than 17% fewer liters over the same distance.

These are use-phase figures: they count fuel burned and electricity drawn, but not fuel production or the manufacture of the car and its battery.

Flight emissions

One 11,000 km long-haul return trip adds 2,874 kg, more than the worked example's car emits in a year.

The factors include radiative forcing, the extra warming from emissions at altitude. Tools that count CO₂ alone report about 41% less, since the DESNZ CO₂-only long-haul factor is 0.15423 kg per passenger-km.

The factors are for an average passenger. DESNZ rates a long-haul business-class seat at 2.9 times an economy one.

Distances, fuel economy and electricity

• Distances are yearly totals, in km or miles. A return flight counts both legs.
• Fuel economy can be L/100 km, km/L, US mpg or UK mpg.
• Home electricity is the household's yearly kWh, split equally among the people in it. For a monthly bill, add up 12 months first.
• Grid factor: outside the UK, use your own grid's figure from your utility or grid operator. It applies to an electric car's charging as well as to the home.

Common mistakes

• Choosing the wrong mpg. 30 US mpg is 7.84 L/100 km, but 30 UK mpg is 9.42 L/100 km. Entering a US figure as UK mpg overstates fuel, and emissions, by 20%; the fuel economy converter shows both.
• Mixing periods. One month of commuting entered as a year's distance understates the car by a factor of 12.
• Dividing everything by household size. Only home electricity is shared. Car distance, flights and diet are your own.
• Comparing with national averages. National per-person figures divide a country's total, industry included, by its population, so they measure something different from these personal activities.

Related calculators

For the money side of the same driving, use the fuel cost calculator. For another household resource, the rainwater harvesting calculator estimates how much water a roof collects.