Car & Vehicle

MPG Calculator

Miles per gallon from distance and fuel - on both the imperial and the US gallon, because they differ by 20%.

5 inputs Free, no sign-up

Your figures

What went in at the second fill-up. That is the amount the trip used, which is why the tank has to be filled to the same point both times.

Both are shown whichever you pick. This one leads.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

"MPG" is not one unit. It is two, and they are 20% apart. An imperial gallon is 4.54609 litres; a US gallon is 3.785411784. The same car is 30 mpg in America and 36 mpg in Britain, having changed nothing.

This page works out both from a distance and a quantity of fuel, and labels each one. A figure quoted as "mpg" with no gallon named cannot be compared with anything.

How to use this calculator

  1. Enter the distance, in kilometres or miles.
  2. Enter the fuel, in litres or either gallon.
  3. Pick which gallon you want the headline figure on.

The units of what you enter and the unit of the answer are independent — you can enter kilometres and litres and read out US mpg, which is the usual case for an Indian driver comparing against an American review.

The formula

km/L      = Distance in km / Fuel in litres
mpg (imp) = km/L x 4.54609 / 1.609344   = km/L x 2.824811
mpg (US)  = km/L x 3.785411784 / 1.609344 = km/L x 2.352146

Both factors are exact rather than measured: a mile is defined as 1,609.344 metres and a US gallon as 231 cubic inches, so neither conversion can drift.

SymbolMeaningUnit
Distance Distance covered km or mi
Fuel used Fuel consumed L, US gal or imp gal

Worked example

250 km on 30 litres is 8.333 km/L:

mpg (imperial) = 8.333 x 2.824811 = 23.54
mpg (US)       = 8.333 x 2.352146 = 19.60

Nearly four miles per gallon apart, describing exactly the same tank.

Notes and limits

  • British and Indian sources, and most European car reviews written in English, mean the imperial gallon. American sources mean the US gallon. When a figure has no flag attached, the number itself is often the clue — a family car at 45 is imperial, at 28 is US.
  • The gallon difference is why an American car that sounds thirsty may be perfectly ordinary and a British one that sounds frugal may be unremarkable.
  • The rest of the world has largely abandoned both in favour of L/100 km, which avoids the argument entirely.
  • The mileage converter moves an existing figure between all four without re-measuring.

What this calculation assumes

  • The distance and the fuel describe the same driving.
  • Both gallons are shown and both are labelled; no figure is presented as bare "mpg".

Frequently asked questions

Is a UK gallon the same as a US gallon?

No. An imperial gallon is 4.54609 litres and a US gallon is 3.785411784 litres - about 20% smaller. A car doing 40 mpg imperial is doing 33.3 mpg US.

How do I convert km/L to mpg?

Multiply km/L by 2.824811 for imperial mpg, or by 2.352146 for US mpg. Both factors come from the exact definitions of the mile and the two gallons.

Which gallon does India use?

Neither, in practice - Indian fuel economy is quoted in km/L. Where an Indian source does use mpg, it is almost always the imperial gallon, following British usage.

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