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MPG Calculator (US, UK, L/100 km)

Enter how far you drove and how much fuel you used to get your fuel economy in miles per gallon, litres per 100 km and kilometres per litre.

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Formula

  • mpg (US) = miles ÷ US gallons, mpg (UK) = miles ÷ UK gallons
  • L/100 km = litres ÷ km × 100
  • km/L = km ÷ litres
  • Exact definitions: 1 mi = 1.609344 km, 1 US gal = 3.785411784 L, 1 UK gal = 4.54609 L.
  • Shortcuts: L/100 km = 235.215 ÷ mpg (US) and L/100 km = 282.481 ÷ mpg (UK).

Worked example

300 miles on 10 US gallons: 300 ÷ 10 = 30 mpg (US). The fuel is 37.854 L and the distance 482.803 km, so L/100 km = 37.854 ÷ 482.803 × 100 = 7.84, km/L = 12.75, and in UK gallons (37.854 ÷ 4.54609 = 8.327) the economy is 300 ÷ 8.327 = 36.03 mpg (UK).

Frequently asked questions

How do I calculate MPG?

Divide the miles you drove by the gallons you used. 300 miles on 10 US gallons is 30 mpg (US).

Why is UK mpg higher than US mpg?

A UK (imperial) gallon is 4.54609 L and a US gallon is 3.785411784 L, so the same car covers more miles per UK gallon. 30 mpg (US) is 36.03 mpg (UK).

How do I convert mpg to L/100 km?

Divide 235.215 by mpg (US), or 282.481 by mpg (UK). 30 mpg (US) gives 235.215 / 30 = 7.84 L/100 km. The conversion also works in reverse.

How do I measure my fuel use accurately?

Fill the tank, reset the trip meter, drive normally, then fill up again and note the litres or gallons added. Use the full distance since the first fill and the fuel from the second fill.

How we calculate

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