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Updated: 14 Jun 2022

Petrol vs diesel fuel calculator

Concerned about rising fuel costs? Confused by mpg claims? Our free calculator helps you work out what you're paying and choose the right engine for your next car.
Martin Pratt
Petrol vs diesel buying guide 447570

With petrol and diesel prices reaching record highs, it pays to know exactly how much your current car is costing you. Our free fuel-cost calculator lets you quickly work out the annual fuel costs for your car and even compare it to another model.

To find out your fuel costs, you'll just need the following:

  • The price per litre for petrol or diesel (whichever your car requires)
  • The mpg (miles per gallon) figure for your car
  • Your estimated total annual mileage (most Which? members drive about 9,000 miles each year)

Of course, price isn't the only thing you should consider when buying a new car. Only cars that are reliable, economical, comfortable, safe and good to drive can become a Which? Best Buy. Head to our best cars for 2022 to find out which we recommend. 

  • Current average fuel prices are available on sites such as the AA, but you can look up prices near you using services such as PetrolPrices.com

Compare fuel costs for two cars

To enter details for second car, click the Add another car for comparison button, then enter the relevant details.

If you're unsure of the mpg for the car you're thinking of buying, be sure to check out our in-depth car reviews.

We ignore manufacturer claims and calculate accurate mpg figures for every car we test.

To obtain these figures, we simulate driving in various locations (city and out-of-town roads, plus motorways) - something the official tests don't do.

As well as providing you with an overall mpg figure, we report separate figures for each driving scenario. This lets you see what the numbers mean for your wallet based on the driving you're most likely to be doing.


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Cut your driving costs

Spending too much money on petrol, diesel or electricity for your car? By making simple adjustments to the way you drive, you can make your fuel go further.

We explain all in our guide on how to save fuel and other money-saving driving tips.