Check a car's MPG

What do the different MPG figures mean?

Cars are quoted with several MPG figures: urban (city), extra-urban (open road) and a combined average. For most drivers the combined figure is the most useful, as it blends town and motorway driving into one number.

The urban figure reflects stop-start city driving, where economy is usually lowest, while the extra-urban figure reflects steadier higher-speed running. The combined figure sits between the two and is the fairest single number for comparing cars.

What is WLTP, and how does it differ from NEDC?

WLTP (Worldwide Harmonised Light Vehicle Test Procedure) is the current official fuel-economy test, used for all new cars since 2017. It replaced the older NEDC test, whose figures were widely seen as unrealistically high.

The old NEDC combined figure was based on a short, gentle laboratory cycle that flattered most cars. WLTP uses a longer, faster and more varied test across four driving phases, so its figures are closer to real-world economy, though still measured in a lab.

Why is real-world MPG lower than the official figure?

Official figures come from a controlled laboratory test, so real-world economy is typically 10–25% lower. Traffic, weather, load, tyre pressures, speed and driving style all reduce the MPG you actually achieve.

The gap has grown over the years, which is exactly why WLTP was introduced. Treat the official MPG as a reliable way to compare cars against each other, not as the figure you will see at the pump.

How do you check a car's MPG by registration?

You check a car's MPG by entering the registration into a vehicle check, which returns the official fuel-economy figures and specification for that exact vehicle.

The Vehicle Certification Agency also publishes official figures for UK cars. Checking the specific car matters because different engines and trims of the same model can vary widely.

1. Enter the registration into the MPG check above.
2. See the official urban, extra-urban and combined MPG figures.
3. Use the combined figure to compare running costs against other cars.

What is a good MPG?

For a petrol car, around 40 MPG or more is good and over 50 MPG is excellent. Diesels tend to go further, with 50+ MPG common and efficient models exceeding 60 MPG.

Bigger, heavier and more powerful cars naturally use more fuel, so judge a car's MPG against similar models rather than in isolation. A strong combined figure is one of the clearest signs of low running costs.

How do you work out fuel running costs from MPG?

Divide your annual mileage by the car's real-world MPG to get gallons used, multiply by 4.546 to convert to litres, then multiply by the price per litre. For many petrol cars the real cost works out around 15–20p per mile.

Because a UK gallon is 4.546 litres, a car doing a real 40 MPG uses about one litre every 8.8 miles. Working from a realistic MPG rather than the headline figure gives you a running cost you can actually budget around.

Why check MPG before buying?

MPG drives one of the biggest ongoing costs of running a car. Checking it confirms the car's economy and helps you compare the true cost of ownership between models.

Fuel economy is only part of the picture, though. Pair it with the car tax check and the history, so a tempting MPG figure is not hiding a clocked or written-off car.