Official fuel economy comes from a laboratory. These figures come from owners. Across 8,216 engines with an owner-reported average, the typical car tested on the old NEDC cycle returns 82% of its official figure and the typical WLTP-tested car returns 94%. Real-world MPG by engine for 776 models across 48 makes, built on more than 319,000 owner submissions, with the official NEDC and WLTP figures alongside so you can see the gap. Free, no sign-up, and you can add your own car’s figure. Why real MPG is lower than the official figure, and the full distribution with a free CSV download.
Miles driven and litres put in, brim to brim, and you get your real MPG. Pick your car and see how it compares with what other owners get.
Fill the tank, note the mileage, drive, fill it to the brim again and put the two figures in. One tank is a guide; three or four are a reliable average.
Looking for the best rather than a particular car? See the most economical used cars on real-world figures, ranked from this dataset.
If you used the Honest John Real MPG section before the site closed in 2026, this is where that information now lives. We rebuilt it from the archived dataset and other sources: the official NEDC and WLTP figures for every engine, the owner-reported averages the archive held, and new submissions from CarAdCheck readers, which keep the averages improving. Each model page links to the archived page it was built from, and to the same car’s known-faults page where we hold one.
CarAdCheck is not affiliated with Honest John or Volkswagen Financial Services. How we rebuilt Real MPG, and how to add your car.
Fill the tank to the brim and note the mileage. Drive as normal, fill it to the brim again and note the litres it took and the miles covered. MPG is miles divided by gallons, and a UK gallon is 4.54609 litres, so MPG = miles ÷ (litres ÷ 4.54609). 312 miles on 34.5 litres is 41.1 mpg. The calculator at the top of this page does the sum, and one tank is a guide; three or four give a reliable average.
Because the gallons are different. A UK (imperial) gallon is 4.546 litres and a US gallon is 3.785 litres, so the same car returns a figure about 20 per cent higher in UK MPG. A calculator built for American drivers will read your car about a fifth low. Everything on this site is in imperial gallons, the same basis as the official UK figures.
There is no single answer, because a small diesel and a large petrol automatic live in different worlds. The useful comparison is with other owners of the same model and engine, which is what every page here holds. As a rule of thumb from the dataset, a car returning within 10 per cent of its owners' average is behaving normally; one well below it on a brimmed tank is usually short trips, town driving or a fault worth checking.
Real MPG is the fuel economy owners actually get, engine by engine, set against the official laboratory figure. The official number is what the car managed on a test cycle; the real number is what people report from the road. The gap is usually 10 to 30 per cent and varies a lot by engine, which is why it is worth checking before you buy.
Honest John closed in August 2026 and its Real MPG section was retired with it. This section is where equivalent data now lives: rebuilt from the archived dataset, with the official NEDC and WLTP figures kept alongside the real-world averages, and reopened for submissions so the figures keep improving. It is free and stays free.
Real average divided by the official combined figure for that engine. Where the official figure is a range, the midpoint is used. Figures marked with an asterisk are measured against the WLTP figure rather than the older NEDC one, which is why they can look higher.
Yes. Every model page has a short form: pick the generation and engine, enter what your car does, say what kind of driving you do. No postcode, no account. Submissions are checked and folded into the averages in batches.
Fuel economy is one line on the running-cost sheet. These cover the rest of buying a used car without getting stung.