Car CO₂ calculator
The same trip in other cars (average size)
Work it out from your MPG
The table figures are the UK fleet average for each size and fuel. If you know what your own car really does, DESNZ's advice is to use it: turn the miles into litres with your fuel economy, then apply the per-litre factor. That is the more accurate figure.
19% less than the UK average petrol car (0.260 kg per mile).
kg CO₂e per mile = 4.54609 ÷ mpg × 2.075 for petrol, or × 2.58354 for diesel. A petrol car doing 45 mpg: 4.54609 ÷ 45 × 2.075 = 0.210 kg per mile, against 0.260 for the average petrol car.
Per-litre factors: DESNZ 2026, Fuels › Liquid fuels, petrol and diesel (average biofuel blend) — the forecourt fuel, with its renewable share counted as DESNZ counts it. A UK gallon is 4.54609 litres. Don't use the CO₂ figure on a V5C or in a brochure here: it is a laboratory figure, and DESNZ says manufacturers' figures need uplifting to real-world driving.
DESNZ 2026 car factors
kg CO₂e per mile, from the government's Greenhouse gas reporting: conversion factors 2026 (flat file revised 31 July 2026). Plug-in hybrids and electric cars include the grid electricity they charge from, with its transmission losses, as DESNZ says to add it.
| Fuel | Small | Medium | Large | Average |
|---|---|---|---|---|
| Petrol | 0.229 | 0.280 | 0.428 | 0.260 |
| Diesel | 0.231 | 0.277 | 0.336 | 0.278 |
| Hybrid | 0.183 | 0.188 | 0.255 | 0.209 |
| Plug-in hybrid | 0.080 | 0.130 | 0.175 | 0.160 |
| Electric | 0.044 | 0.045 | 0.049 | 0.048 |
| Fuel not known | 0.230 | 0.279 | 0.366 | 0.267 |
| LPG | — | 0.280 | 0.428 | 0.315 |
| CNG | — | 0.248 | 0.378 | 0.279 |
The same, per km:
| Fuel | Small | Medium | Large | Average |
|---|---|---|---|---|
| Petrol | 0.143 | 0.174 | 0.266 | 0.162 |
| Diesel | 0.143 | 0.172 | 0.209 | 0.173 |
| Hybrid | 0.114 | 0.117 | 0.158 | 0.130 |
| Plug-in hybrid | 0.050 | 0.081 | 0.109 | 0.099 |
| Electric | 0.027 | 0.028 | 0.031 | 0.030 |
| Fuel not known | 0.143 | 0.173 | 0.228 | 0.166 |
| LPG | — | 0.174 | 0.266 | 0.196 |
| CNG | — | 0.154 | 0.235 | 0.173 |
Rounded to three places here; the calculator and the copied figure use DESNZ's five. — means DESNZ publishes no figure (there is no small LPG or CNG car in its data). Tailpipe emissions, plus grid electricity for plug-ins; the emissions of producing the fuel or power upstream ("well-to-tank") are a separate DESNZ table and aren't included, as in DESNZ's headline factors.
What counts as small, medium and large
- Small: Petrol, LPG or CNG up to a 1.4-litre engine; diesel up to 1.7 litres; others (hybrids, EVs) of a similar size - market segment A or B.
- Medium: Petrol, LPG or CNG from 1.4 to 2.0 litres; diesel from 1.7 to 2.0 litres; others of a similar size - generally market segment C.
- Large: Petrol, LPG, CNG or diesel over 2.0 litres; others of a similar size - generally market segment D and above.
- Average: The UK fleet average, for when the size is not known.
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Petrol, diesel, hybrid or electric?
Per mile, an average diesel car (0.278 kg) emits a little more than an average petrol one (0.260 kg) on DESNZ's 2026 figures, though a diesel usually covers more miles on a litre — the gap depends on the cars. A self-charging hybrid brings it down to 0.209 kg. A plug-in hybrid's 0.160 kg assumes the UK average split of petrol and electric miles, so it depends on how often it's plugged in. An electric car emits nothing from the tailpipe: its 0.048 kg a mile is the grid electricity it charges from, which falls as the grid gets cleaner.
Size matters as much as fuel. A large petrol car (0.428 kg a mile) emits nearly twice what a small one does (0.229 kg).
What these figures include
They are the UK Government's greenhouse gas conversion factors for company reporting, published by DESNZ every year and used for SECR returns and carbon footprints. They're real-world averages across the cars on UK roads — not the laboratory figure on a V5C — and cover the carbon dioxide, methane and nitrous oxide from the exhaust, as CO₂e. Producing the fuel or electricity upstream, and building the car, are reported separately and aren't included.
For a year, multiply by your mileage: 7,100 miles, the average for a car in England, comes to 1.85 tonnes in an average petrol car — about 84 trees' worth of a year's absorption.
Source: DESNZ, Greenhouse gas reporting: conversion factors 2026 (flat file revised 31 July 2026) — Passenger vehicles, UK electricity for EVs, UK electricity T&D for EVs and Fuels; annual mileage: DfT National Travel Survey 2025, table NTS0901 (all cars, England).
Related reading
Frequently asked questions
How do I calculate a car’s CO₂ emissions per mile?
Multiply the miles by the government factor for the car's fuel and size — an average petrol car is 0.260 kg CO₂e a mile — or, more accurately, start from its real fuel economy: 4.54609 ÷ MPG gives litres per mile, and a litre of petrol emits 2.075 kg CO₂e (diesel 2.584). A 45 mpg petrol car: 4.54609 ÷ 45 × 2.075 = 0.210 kg a mile.
How much CO₂ does an electric car produce per mile?
Nothing from the exhaust. Charging an average electric car from the UK grid comes to about 0.048 kg CO₂e a mile (0.030 per km) on DESNZ's 2026 figures, including the electricity lost in transmission — under a fifth of an average petrol car, and falling as the grid decarbonises.
Petrol vs diesel per mile?
On DESNZ's 2026 fleet averages a diesel car emits 0.278 kg CO₂e a mile and a petrol car 0.260. To compare two particular cars, use their real MPG in the calculator above: diesel carries more carbon per litre (2.584 kg against 2.075) but usually goes further on it.
How much CO₂ does a car produce in a year?
An average petrol car driven 7,100 miles — the average for a car in England — emits about 1.85 tonnes CO₂e. Put your own mileage into the calculator for yours.
Why is my car’s official CO₂ figure lower?
The g/km on a V5C or in a brochure comes from a laboratory test, and real driving burns more fuel. DESNZ’s factors are real-world UK averages, and its guidance says manufacturers’ figures need uplifting before they’re used for reporting. Your car’s actual MPG is the best evidence for your own car.
Does this include producing the fuel?
No. Like DESNZ’s headline factors, these cover the exhaust — and, for plug-in cars, the electricity they charge from. The emissions of extracting, refining and delivering the fuel (“well-to-tank”) are a separate DESNZ table.