Fuel Consumption Calculator
Work out your car’s real fuel consumption from a fill-up – in L/100 km, km/L, litres per mil and US or UK mpg.
Fill the tank completely both times for an accurate figure, and measure over at least a few hundred kilometres. Real-world consumption is usually higher than official WLTP or EPA test figures.
About this tool
Fill the tank, drive, fill it again and enter the distance on the trip meter and the fuel you put in. You get your real-world consumption in litres per 100 km, kilometres per litre, litres per mil and miles per gallon (US and UK). Use kilometres and litres, miles and US gallons, or the UK mix of miles and litres. Add what you paid to see the cost per kilometre or mile.
Frequently asked questions
Fill the tank to the top and reset the trip meter. Drive as normal, then fill up again and note the litres. Divide the litres by the kilometres and multiply by 100: 42 litres after 650 km is 42 ÷ 650 × 100 = 6.46 L/100 km, or 650 ÷ 42 = 15.5 km/L.
Convert the litres to imperial gallons by dividing by 4.54609, then divide the miles by the gallons. 45 litres is 9.90 gallons, so 400 miles on 45 litres is 400 ÷ 9.90 = 40.4 mpg (UK). Choose “Miles and litres (UK)” and the calculator does this for you.
Official figures come from standard laboratory tests (WLTP in Europe, EPA in the US) at set speeds and temperatures. Short trips, cold weather, motorway speeds, roof boxes, heavy loads and underinflated tyres all raise real-world fuel use above the test value.
The longer the better. The pump cuts off at a slightly different level each time, so an error of one litre over 300 km changes the result by about 0.3 L/100 km, but over 1,000 km by only 0.1 L/100 km. Averaging several fill-ups gives the most reliable figure.
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