Global Fuel CalculatorMPG and fuel cost calculator for the United Kingdom
The UK runs on a genuinely odd combination: fuel is sold in litres, distance is measured in miles, and fuel economy is quoted in miles per imperial gallon. That means working out your MPG by hand requires converting litres to imperial gallons first, which is exactly the step most people get wrong. This calculator is configured for it — litres in, miles in, imperial MPG out.
The imperial gallon is 4.54609 litres, appreciably larger than the US gallon of 3.785 litres. A car achieving 45 MPG in British terms would be quoted as about 37 MPG in American terms for identical consumption. Every figure on this page is imperial.
Cost per mile is shown alongside the MPG result, which is usually the more practical number: it is what mileage claims, lease comparisons and company car decisions are built on. Add a journey distance in the trip field and the calculator estimates the fuel and the cost for that drive before you set off.
Work out your numbers
Indicative starting price only, last reviewed 2026-01. Enter your own pump price for an accurate result.
How fuel economy is measured here
United Kingdom works in miles for distance and litres for fuel, with economy normally quoted as MPG (imperial). The calculator above is set that way by default, and the unit selectors let you switch if you need a different basis.
| Unit | Typical local figure |
|---|---|
| L/100km | 8.00 |
| km/L | 12.50 |
| MPG (US) | 29.40 |
| MPG (imperial) | 35.31 |
Local context
Petrol and diesel are sold by the litre with prices displayed in pence, typically to one tenth of a penny. Supermarket forecourts are usually a few pence cheaper than motorway services, where prices can run substantially higher.
Official economy figures are now published under the WLTP test cycle, which is more realistic than the older NEDC standard but still optimistic for most drivers. Cost per mile, usually expressed in pence, is the figure that matters for mileage claims and company car comparisons, and this calculator gives it directly.
Common questions
How do I convert litres to MPG?
Divide the litres you put in by 4.54609 to get imperial gallons, then divide your miles by that figure. If you added 45 litres and drove 420 miles, that is 9.9 imperial gallons, giving about 42.4 MPG. This calculator does the conversion for you so the litre-to-gallon step cannot go wrong.
Is UK MPG the same as US MPG?
No. UK MPG uses the imperial gallon of 4.546 litres and US MPG uses the US gallon of 3.785 litres. UK figures are about twenty percent higher for the same actual consumption, which is why American reviews of the same car appear to report worse economy.
How do I work out pence per mile?
Divide the total cost of the fuel by the miles it covered, then multiply by one hundred. The calculator shows cost per mile directly, which is the figure most employers and lease comparisons ask for.
Why does my car miss its official WLTP figure?
WLTP is measured under controlled laboratory conditions at fixed temperatures with no passengers beyond the driver and no accessories running. Cold weather, short journeys, motorway speeds above 70 mph and a full car all raise real consumption. Missing the official figure by ten to twenty percent is typical.
Does driving at 70 rather than 80 really save fuel?
Substantially. Aerodynamic drag rises with the square of speed, so the power needed to maintain pace climbs steeply above about 60 mph. Dropping from 80 to 70 mph on a long motorway run commonly improves consumption by well over ten percent.
What about L/100km figures in European reviews?
L/100km is the continental standard and works in the opposite direction to MPG — lower is better. This calculator displays the L/100km equivalent next to your imperial MPG so you can compare a UK review with a German or French one without converting.