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Updated: 29 Dec 2021

Petrol vs diesel fuel calculator

Does buying diesel really save you money? Or is petrol the better buy? Here's our fuel-cost calculator to help you choose the right engine for your car.
Martin Pratt
Petrol vs diesel buying guide 447570

Our fuel-cost calculator below lets you quickly work out and compare the annual fuel costs between two cars (petrol and diesel, or otherwise).

We also report our own mpg figures for every car we test.

Our rigorous car tests are based on real-world driving. We simulate 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 each figure separately. That way you can actually see what the numbers mean for your wallet based on your typical type of driving. 

But fuel 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.

Go to our best cars for 2021 to find out which we recommend. 

For the full lowdown on whether you should invest in a petrol or diesel car, here's our dedicated guide on how to choose between petrol and diesel cars.

Petrol vs diesel fuel-cost calculator: is the diesel premium worth it?

  • Click the Add another car for comparison option.
  • Add the fuel-economy figures for two cars. 
  • Add your annual mileage (most Which? members drive about 9,000 miles each year). 

You can look up current fuel prices on sites such as the AA and PetrolPrices.com - or contact your local garage.

Looking for a new car? Head straight to our new and used car reviews

If you'd prefer to stick with your existing car, give the bodywork a new lease of life by using one of our best car scratch remover kits

Petrol car annual running costs

Below, we’ve crunched the numbers to calculate annual fuel costs for three of the most popular models across the small, medium and SUV car classes. Given the downturn in demand for diesel cars, we’ve focused solely on the petrol models we’ve tested.

Each of our comprehensive car reviews contains independent, lab-tested fuel economy data for every engine version we’ve tested. You can easily compare fuel costs as we tell you how much each engine will set you back in monthly and annual fuel bills. 

Only economical, reliable models make it into our pick of the best cars.