Real MPG calculator

MPG stands for miles per gallon and, as this name suggests, it’s the number of miles that a car can cover on a gallon of petrol or diesel. However, the actual figure will vary dramatically depending on traffic and weather conditions, and how smoothly or aggressively the car is being driven.

What Car?’s Real MPG fuel tests are conducted on a rolling road, under strictly controlled laboratory conditions. This means our tests are repeatable, because outside variables such as weather and traffic don't affect the results. Tests are carried out at Millbrook Proving Ground, a centre used for regulatory approved vehicle emissions testing. Millbrook has the latest equipment for testing vehicles in a highly scientific manner.

Like What Car?'s Real MPG tests, the official Government tests are conducted on a rolling road, under laboratory conditions. However, these official tests don't require the engine to be worked as hard, so the resulting figures often don't reflect what you're likely to be able to achieve in the real world.

What Car?'s Real MPG figures show what you can typically expect from a car when it's driven sensibly and within speed limits, but without resorting to unusual fuel-saving measures or any 'hypermiling' techniques. Real MPG results are 4% lower on average than the latest WLTP official figures and 24% lower than the old NEDC figures which were used up until 1 September 2018.

The most efficient cars on sale today average almost 60mpg in What Car?’s Real MPG test, but anything over 50mpg is impressive.

It’s unlikely you’ll return the kind of fuel economy figures outlined in your car’s handbook or in brochures. In fact, our Real MPG testing has found that, on average, real-world economy is some 4% lower than the latest WLTP official figures - and a massive 24% lower than the old NEDC figures.

There can sometimes be a discrepancy between the economy your trip computer shows and the actual economy, too. The differences here vary from car to car.

While you can search for the fuel economy you can realistically expect a car to return online using What Car?’s Real MPG calculator, you can also track your own car’s fuel economy using some simple arithmetic. Firstly, fill your car’s fuel tank to the brim and note your car’s mileage or reset the trip computer. The next time you visit a fuel station, fill your car to the brim and note how much fuel it’s taken.

Now grab a calculator and convert the number of litres you’ve bought into imperial gallons by multiplying it by 0.219. Calculate the distance covered by subtracting the starting mileage from your current mileage. Then divide the miles you’ve covered by the gallons of fuel you’ve put in.

An engine burns less fuel at low revs, so changing up to a higher gear earlier and avoiding hard acceleration will improve your fuel economy. Simple steps such as closing your car's windows and clearing out the boot to reduce weight will also help. For more fuel saving tips, click here.

All new cars registered from 1 September 2018 are tested under the Worldwide Light Vehicle Test Procedure (WLTP), which is designed to better reflect real-world driving conditions than the old New European Driving Cycle (NEDC) test. We explain more in our WLTP and RDE advice feature.

The official WLTP laboratory test is supplemented by Real Driving Emissions (RDE) testing which, as its name suggests, takes place on public roads. However, because RDE figures are less repeatable, they're currently only being used to verify certain pollutants, such as nitrogen oxides (NOx). Diesel cars that have been verified aren't subject to the 4% benefit-in-kind (BIK) tax surcharge that other diesels are. Our best company cars feature runs down the top choices.

To convert the l/100km figure that’s used in continental Europe into the imperial MPG figure used in the UK, you simply divide it by 282.5.

L/100km to U.K. mpg Conversion Table