# Personal carbon footprint calculator

> Carbon footprint calculator: yearly tonnes of CO₂e from driving, flights, train and bus, home electricity and diet, using UK government emission factors.

Interactive version: https://www.calcopenly.com/earth/carbon-footprint-calculator
Subject: Weather, earth and fun calculators

The footprint is a sum of activity × emission factor: litres of fuel burned (distance ÷ fuel economy), passenger-kilometres by air, rail and bus, your share of household electricity, and a daily diet figure × 365. Transport and electricity factors are the UK government's 2024 greenhouse gas conversion factors (DESNZ); diet figures come from Scarborough et al. (2014), who analysed the diets of UK adults in the EPIC-Oxford cohort.

It shows which change would cut the most. The defaults (12,000 km in a petrol car at 7 L/100 km, 2,000 km of short-haul flights, a medium-meat diet and half of a 2,700 kWh household) add up to 4.57 t CO₂e a year, with diet the largest part at 2,055 kg.

CO₂e counts methane and nitrous oxide by their warming effect relative to CO₂, and the flight factors include the extra warming from emissions at altitude. Gas heating, goods, services and the manufacture of the car are left out, so the total covers only part of a full footprint.

## Inputs

- **Car distance per year**
- **Car fuel** (options: Petrol, Diesel, Electric, No car)
- **Fuel economy**
- **Electricity use**
- **Domestic flights, distance per year**
- **Short-haul flights (under 3,700 km each), distance per year**
- **Long-haul flights (over 3,700 km each), distance per year**
- **Train distance per year**
- **Bus distance per year**
- **Home electricity use**
- **People in the household**
- **Electricity grid** (options: UK grid 2024 (0.225 kg/kWh), Enter my grid's factor)
- **Grid emission factor**: Your utility or national grid operator publishes this; it also applies to an electric car.
- **Diet** (options: High meat (100 g a day or more), Medium meat (50–99 g a day), Low meat (under 50 g a day), Fish but no meat, Vegetarian, Vegan)

## Results

- Yearly footprint (t CO₂e) — main result
- Car (kg CO₂e)
- Flights (kg CO₂e)
- Train and bus (kg CO₂e)
- Home electricity (your share) (kg CO₂e)
- Diet (kg CO₂e)
- Largest source

## Formula

$$
E = \sum_i \text{activity}_i \times \text{factor}_i
$$

## Worked examples

### Petrol car, 10,000 km at 7 L/100 km

- Car distance per year: 10,000 km
- Car fuel: Petrol
- Fuel economy: 7 L/100 km
- Domestic flights, distance per year: 0 km
- Short-haul flights (under 3,700 km each), distance per year: 2000 km
- Long-haul flights (over 3,700 km each), distance per year: 0 km
- Train distance per year: 1000 km
- Bus distance per year: 500 km
- Home electricity use: 2700 kWh a year
- People in the household: 2
- Electricity grid: UK grid 2024 (0.225 kg/kWh)
- Diet: Medium meat (50–99 g a day)
- **Car: 1,459 kg CO₂e**
- Checked against: 700 L × 2.0844 kg CO₂e/L (DESNZ 2024, petrol average biofuel blend) = 1459.08 kg, Python decimal

### Diesel car, 20,000 km at 5 L/100 km

- Car distance per year: 20,000 km
- Car fuel: Diesel
- Fuel economy: 5 L/100 km
- Domestic flights, distance per year: 0 km
- Short-haul flights (under 3,700 km each), distance per year: 2000 km
- Long-haul flights (over 3,700 km each), distance per year: 0 km
- Train distance per year: 1000 km
- Bus distance per year: 500 km
- Home electricity use: 2700 kWh a year
- People in the household: 2
- Electricity grid: UK grid 2024 (0.225 kg/kWh)
- Diet: Medium meat (50–99 g a day)
- **Car: 2,513 kg CO₂e**
- Checked against: 1000 L × 2.51279 kg CO₂e/L (DESNZ 2024, diesel average biofuel blend)

### US units: 10,000 miles at 30 mpg

- Car distance per year: 10,000 mi
- Car fuel: Petrol
- Fuel economy: 30 mpg (US)
- Domestic flights, distance per year: 0 km
- Short-haul flights (under 3,700 km each), distance per year: 2000 km
- Long-haul flights (over 3,700 km each), distance per year: 0 km
- Train distance per year: 1000 km
- Bus distance per year: 500 km
- Home electricity use: 2700 kWh a year
- People in the household: 2
- Electricity grid: UK grid 2024 (0.225 kg/kWh)
- Diet: Medium meat (50–99 g a day)
- **Car: 2,630 kg CO₂e**
- Checked against: 10000/30 US gal × 3.785411784 L = 1261.80 L × 2.0844 = 2630.10 kg, Python decimal

### One long-haul return trip of 11,000 km in total

- Car distance per year: 12,000 km
- Car fuel: Petrol
- Fuel economy: 7 L/100 km
- Domestic flights, distance per year: 0 km
- Short-haul flights (under 3,700 km each), distance per year: 0 km
- Long-haul flights (over 3,700 km each), distance per year: 11,000 km
- Train distance per year: 1000 km
- Bus distance per year: 500 km
- Home electricity use: 2700 kWh a year
- People in the household: 2
- Electricity grid: UK grid 2024 (0.225 kg/kWh)
- Diet: Medium meat (50–99 g a day)
- **Flights: 2,874 kg CO₂e**
- Checked against: 11 000 passenger-km × 0.26128 kg CO₂e (DESNZ 2024, long-haul average passenger, with radiative forcing)

### Electric car on the UK grid

- Car distance per year: 15,000 km
- Car fuel: Electric
- Electricity use: 17 kWh/100 km
- Domestic flights, distance per year: 0 km
- Short-haul flights (under 3,700 km each), distance per year: 2000 km
- Long-haul flights (over 3,700 km each), distance per year: 0 km
- Train distance per year: 1000 km
- Bus distance per year: 500 km
- Home electricity use: 2700 kWh a year
- People in the household: 2
- Electricity grid: UK grid 2024 (0.225 kg/kWh)
- Diet: Medium meat (50–99 g a day)
- **Car: 575 kg CO₂e**
- Checked against: 2550 kWh × (0.20705 + 0.01830) kg CO₂e/kWh (DESNZ 2024 generation plus T&D) = 574.6425 kg

### Vegan with no travel or electricity

- Car distance per year: 12,000 km
- Car fuel: No car
- Domestic flights, distance per year: 0 km
- Short-haul flights (under 3,700 km each), distance per year: 0 km
- Long-haul flights (over 3,700 km each), distance per year: 0 km
- Train distance per year: 0 km
- Bus distance per year: 0 km
- Home electricity use: 0 kWh a year
- People in the household: 2
- Electricity grid: UK grid 2024 (0.225 kg/kWh)
- Diet: Vegan
- **Yearly footprint: 1.05 t CO₂e**
- **Diet: 1,055 kg CO₂e**
- **Largest source: Diet**
- Checked against: 2.89 kg CO₂e/day (Scarborough et al. 2014, vegans) × 365 = 1054.85 kg

## Questions

### What is the average carbon footprint per person?

CO₂ emissions from fossil fuels and industry averaged 4.7 tonnes per person worldwide in 2024 (Global Carbon Budget 2025, via Our World in Data): 14.2 t in the United States, 8.7 t in China, 4.5 t in the United Kingdom and 2.2 t in India. Those are national totals including industry and excluding other greenhouse gases, so they do not compare directly with the personal activities added up here.

### How much CO₂ does a flight produce?

DESNZ 2024 gives 0.26128 kg CO₂e per passenger-km for an average long-haul passenger including radiative forcing, or 0.15423 kg for the CO₂ alone. An 11,000 km return trip therefore adds 2,874 kg. Seat class matters: a long-haul business-class seat is rated at 0.58028 kg per km, 2.9 times the economy figure of 0.20011 kg.

### How much CO₂ does a car emit per litre of fuel?

DESNZ 2024 gives 2.0844 kg CO₂e per litre of petrol and 2.51279 kg per litre of diesel, both for the average UK biofuel blend. A petrol car using 7 L/100 km burns 840 litres over 12,000 km, which is 1,751 kg a year. These are tailpipe figures; fuel production and the car's manufacture are extra.

### Does an electric car have a lower carbon footprint?

Per kilometre driven, yes on the UK grid. At the 2024 factor of 0.22535 kg CO₂e per kWh including transmission losses (DESNZ), an electric car using 17 kWh per 100 km emits 38 g per km, against 146 g per km for a petrol car at 7 L/100 km. Battery and vehicle manufacture are outside this comparison.

### How much does diet change a carbon footprint?

By up to about 1.6 tonnes a year. Scarborough et al. (2014) measured 7.19 kg CO₂e a day for UK high-meat diets and 2.89 kg for vegan diets, both scaled to 2,000 kcal. Over a year that is 2,624 kg against 1,055 kg. A medium-meat diet (50–99 g a day) comes to 2,055 kg.

### How accurate is the personal carbon footprint calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 7 worked examples whose answers come from independent sources; for example, “Petrol car, 10,000 km at 7 L/100 km” is checked against 700 L × 2.0844 kg CO₂e/L (DESNZ 2024, petrol average biofuel blend) = 1459.08 kg, Python decimal.

### Where does the method come from?

UK DESNZ — Greenhouse gas reporting: conversion factors 2024 (flat file v1.1); P. Scarborough et al., “Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK”, Climatic Change 125 (2014) 179–192.

## Sources

- [UK DESNZ — Greenhouse gas reporting: conversion factors 2024 (flat file v1.1)](https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2024)
- [P. Scarborough et al., “Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK”, Climatic Change 125 (2014) 179–192](https://doi.org/10.1007/s10584-014-1169-1)