What's your real MPG?

• Take part in fuel economy survey
• Work out your average MPG in Two-Tank Test
• Email us your results by June 30

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What Car? would like you to take part in the biggest-ever fuel economy survey in Britain.

We're asking all our readers to take part in a wide-ranging investigation to establish the real-world mpg figures for as many makes and models as possible.

Take part in our 'Two-Tank test' and send in your results. It's quite simple - you need to:

1. Fill up your tank to the brim.
2. Drive until you are quarter full or under and record the amount of miles completed.
3. Fill up again, measuring exactly how much you took to fill it up.
4. Drive until you are quarter full or under.
5. Fill up again recording exactly how much fuel you used.
6. Then calculate your car's fuel consumption (see below).
7. E-mail us with your results by clicking here

NB: please remember to tell us what car you drive (the exact model – stating engine size, power output, whether it's diesel, petrol, hybrid and trim level - for example, Ford Focus 1.6 Studio 3-door), your contact details and whether your journeys were mostly town driving or motorway miles. Please also indicate whether you drive a manual or automatic.

We hope to establish how much real-world figures differ from the official fuel figures in the biggest-ever test conducted in the UK. Results need to be in by the June 30.

• How to calculate your average MPG
1. Determine the total mileage during the test.
2. Take the total number of litres you have used and divide by 4.5461 to calculate the total number of gallons used.
3 Divide the mileage by the gallons to find out your total mpg.