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Convert mpg to L/100 km

Miles per gallon to liters per 100 km, with US and UK gallons shown side by side.

Miles per gallon to liters per 100 km

mpg (US)

Gallon

30 miles per US gallon equals

7.840486111 L/100 km

US gallon: 3.785411784 liters. Rounded for display; choose more digits under Precision to see more.

How it is worked out

  1. Fuel per distance is the reciprocal of distance per fuel: L/100 km = 235.2145833 ÷ mpg (US).
  2. In kilometers per liter: 30 mpg (US) = 12.75431122 km/L, and 12.75431122 km/L = 7.840486111 L/100 km.

US and UK gallons side by side

  • 30 mpg (US) ≈ 7.840486111 L/100 km

    US gallon: 3.785411784 liters. This is the mpg on American window stickers.

  • 30 mpg (UK) ≈ 9.416031211 L/100 km

    UK (imperial) gallon: 4.54609 liters, about 20% bigger than the US gallon. This is the mpg quoted in the United Kingdom.

The two answers differ because a UK gallon holds about 20% more fuel than a US gallon. A car that does 30 mpg on UK gallons is thirstier than one that does 30 mpg on US gallons.

Common fuel economies in mpg and L/100 km

The same mpg figure is a different fuel use in a US car and a UK car, because the gallons differ.

Common fuel economies in mpg and L/100 km. Values are rounded to 2 decimal places.
Miles per gallon (mpg)L/100 km with US gallonsL/100 km with UK gallons
1023.5228.25
1515.6818.83
2011.7614.12
259.4111.3
307.849.42
356.728.07
405.887.06
455.236.28
504.75.65
603.924.71

Values are rounded to 2 decimal places. The calculation above is exact.

At a glance

Formula
US: L/100 km = 235.2145833 ÷ mpg. UK: L/100 km = 282.4809363 ÷ mpg.
Which gallon
mpg means a different thing in the US and the UK, so the page opens on US gallons and always shows the UK answer beside it.
Examples
30 mpg (US) = 7.84 L/100 km. 30 mpg (UK) = 9.42 L/100 km. 40 mpg (US) = 5.88 L/100 km.
Direction
Higher mpg is better, but lower L/100 km is better. A bigger mpg gives a smaller L/100 km.
Also shown
A table from 10 to 60 mpg with the US and UK answers on each row.
Price
Free, no sign-up. Runs in your browser.

How to do it

  1. 1

    Enter the mpg figure

    Type it in Value. The box starts at 30.

  2. 2

    Choose the gallon

    US gallon for American figures and UK gallon for British ones. If you are not sure, read both answers in the list below the result.

  3. 3

    Read liters per 100 km

    The working shows the constant divided by your number.

  4. 4

    Go the other way

    Press the swap button to turn L/100 km into mpg. The same sum works in both directions.

The formula

Divide 235.2145833 by the mpg figure to get liters per 100 km, if the mpg uses US gallons. 30 mpg gives 235.2145833 ÷ 30 = 7.84 L/100 km.

Here is where the constant comes from. One mile per US gallon is 1.609344 km for 3.785411784 liters, so 100 km takes 100 ÷ 1.609344 miles, which is 62.1371 miles, and a car that does one mile per gallon would burn 62.1371 gallons, or 235.2145833 liters, over that distance. Dividing by the mpg figure scales it. For UK gallons replace 3.785411784 with 4.54609 and the constant becomes 282.4809363. The calculation is a reciprocal, so a bigger mpg number gives a smaller L/100 km one.

Which gallon is your mpg?

This is the main source of wrong answers. A UK gallon is 20% bigger than a US gallon, so a car rated 30 mpg in the United Kingdom uses more fuel per kilometer than one rated 30 mpg on an American label.

  • A figure from an American source, such as a window sticker or a US review, is in US gallons.
  • A figure from a British magazine, a UK car brochure or a UK listing is in UK gallons.
  • If the source does not say, think about where it comes from. Do not guess from the number.

The two answers differ by the same 20%: 25 mpg is 9.41 L/100 km in US units and 11.30 in UK units. The table under the converter lists both for 10 to 60 mpg.

Using the answer: fuel for a trip

Liters per 100 km is easy to scale. Fuel for a trip is the distance in kilometers divided by 100, times the L/100 km figure. A 300 km trip at 30 mpg (US), which is 7.84 L/100 km, takes 3 × 7.84 = 23.5 liters. At 30 mpg (UK), 9.42 L/100 km, the same trip takes 28.2 liters. Multiply by the price per liter to get a cost.

Measured fuel economy depends on speed, load, temperature and traffic, so treat the answer as an estimate based on the figure you entered.

Lower is better

Because L/100 km is the fuel used, a smaller number means a thriftier car. A car that goes from 35 mpg (US) to 40 mpg (US) moves from 6.72 to 5.88 L/100 km. The fuel economy converter explains why equal steps in mpg are not equal steps in fuel saved.

Questions people ask

What is 25 mpg in L/100 km?

9.41 L/100 km with US gallons, or 11.30 L/100 km with UK gallons.

What is 40 mpg in L/100 km?

5.88 L/100 km with US gallons, or 7.06 L/100 km with UK gallons.

How do I convert L/100 km to mpg?

Divide the same constant by your L/100 km figure: 235.2145833 for US mpg, 282.4809363 for UK mpg. 8 L/100 km is 29.4 mpg (US). Press the swap button to do it here.

Why does one mpg figure give two answers?

Because the US and the UK use different gallons. This page shows both, and you pick the one that matches where your figure came from.

Is a higher mpg or a lower L/100 km better?

Both mean the car uses less fuel. They move in opposite directions, because one counts distance per fuel and the other fuel per distance.

How much fuel will a trip use?

Distance in kilometers divided by 100, multiplied by L/100 km. For 300 km at 7.84 L/100 km that is 23.5 liters.

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