
Which? Car Survey 2026: now open
Tell us about your car and be in with a chance of winning £2,500 (T&Cs apply). Survey closes 10am on 17 June, 2026.
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Fuel economy is typically measured in miles per gallon, but at the fuel pump petrol and diesel is measured in litres. Using our free tool, you can convert between the two so you can more accurately judge your car's fuel economy.
Our lab tests discover a car’s true mpg by using a rolling road, which means every car can be tested in the exact same way, and the same environment.
The test roads imitate city, out-of-town and motorway driving for extended periods of time - something the official tests don't do - which allows you to see how the mpg could affect your pocket depending on the roads you typically drive on.
Looking to cut your running costs? We show you how in our money-saving driving tips guide

Tell us about your car and be in with a chance of winning £2,500 (T&Cs apply). Survey closes 10am on 17 June, 2026.
Take part nowOur tests reveal that most official fuel-economy figures are inaccurate.
To discover your car’s true mpg, try using the Which? car fuel calculator. It allows you to work out the amount of fuel you used on recent trips, and see exactly how much you ended up paying for single journeys.
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