What Fuel Economy Converter does
30 mpg is 7.84 L/100 km if the gallon is American and 9.42 L/100 km if it is British, so the first thing to settle is which gallon your figure uses. This converter takes a figure in miles per US gallon, miles per UK (imperial) gallon, litres per 100 km or kilometres per litre and shows all four together, along with the fuel used over 100 miles and a table of nearby values. It uses the exact definitions: a US gallon is 3.785411784 litres, an imperial gallon is 4.54609 litres and a mile is 1.609344 km. Results are rounded to two decimal places.
MPG to L/100 km chart for US and UK gallons
Read across from the mpg figure. Use the US columns for American figures and the UK columns for British ones; mixing them up puts the answer out by about 20%.
| mpg | US mpg in L/100 km | US mpg in km/L | UK mpg in L/100 km | UK mpg in km/L |
|---|---|---|---|---|
| 10 | 23.52 | 4.25 | 28.25 | 3.54 |
| 15 | 15.68 | 6.38 | 18.83 | 5.31 |
| 20 | 11.76 | 8.5 | 14.12 | 7.08 |
| 25 | 9.41 | 10.63 | 11.3 | 8.85 |
| 30 | 7.84 | 12.75 | 9.42 | 10.62 |
| 35 | 6.72 | 14.88 | 8.07 | 12.39 |
| 40 | 5.88 | 17.01 | 7.06 | 14.16 |
| 45 | 5.23 | 19.13 | 6.28 | 15.93 |
| 50 | 4.7 | 21.26 | 5.65 | 17.7 |
| 55 | 4.28 | 23.38 | 5.14 | 19.47 |
| 60 | 3.92 | 25.51 | 4.71 | 21.24 |
| 65 | 3.62 | 27.63 | 4.35 | 23.01 |
| 70 | 3.36 | 29.76 | 4.04 | 24.78 |
Every value is this converter's output, rounded to two decimals with trailing zeros dropped.
L/100 km to mpg chart
Going the other way, from a litres per 100 km figure to both kinds of mpg and to km per litre.
| L/100 km | US mpg | UK mpg | km/L |
|---|---|---|---|
| 3 | 78.4 | 94.16 | 33.33 |
| 4 | 58.8 | 70.62 | 25 |
| 4.5 | 52.27 | 62.77 | 22.22 |
| 5 | 47.04 | 56.5 | 20 |
| 5.5 | 42.77 | 51.36 | 18.18 |
| 6 | 39.2 | 47.08 | 16.67 |
| 6.5 | 36.19 | 43.46 | 15.38 |
| 7 | 33.6 | 40.35 | 14.29 |
| 7.5 | 31.36 | 37.66 | 13.33 |
| 8 | 29.4 | 35.31 | 12.5 |
| 9 | 26.13 | 31.39 | 11.11 |
| 10 | 23.52 | 28.25 | 10 |
| 12 | 19.6 | 23.54 | 8.33 |
| 15 | 15.68 | 18.83 | 6.67 |
| 20 | 11.76 | 14.12 | 5 |
The conversion formulas and where 235.215 comes from
L/100 km = 235.215 ÷ mpg (US) | L/100 km = 282.481 ÷ mpg (UK) | L/100 km = 100 ÷ km/L
One mile per US gallon is 1.609344 km on 3.785411784 litres, which is 0.425144 km/L. Fuel per 100 km is 100 divided by km/L, so 100 ÷ 0.425144 = 235.2146 for one mpg, and the result for any other figure is 235.2146 divided by it. With the imperial gallon of 4.54609 litres, one mpg is 0.354006 km/L and the constant becomes 282.4809. Because the relationship is a division, the same constant converts back: mpg = 235.215 ÷ L/100 km. To switch between the two kinds of mpg, multiply US mpg by 1.20095 to get UK mpg, or multiply UK mpg by 0.832674 to get US mpg.
Worked fuel economy conversions
An American car review read in Europe
Fuel economy figure: 25; Unit of that figure: Miles per US gallon
9.41 L/100 km; 30.02 UK mpg; 10.63 km/L; 4 US gallons per 100 miles
A British mpg figure for a US reader
Fuel economy figure: 50; Unit of that figure: Miles per UK gallon
5.65 L/100 km; 41.63 US mpg; 17.7 km/L; 2 UK gallons per 100 miles
A European consumption figure
Fuel economy figure: 6.5; Unit of that figure: Litres per 100 km
36.19 US mpg; 43.46 UK mpg; 15.38 km/L; 10.46 litres per 100 miles
A km per litre figure, as quoted in India or Japan
Fuel economy figure: 20; Unit of that figure: Kilometres per litre
5 L/100 km; 47.04 US mpg; 56.5 UK mpg
A heavy vehicle
Fuel economy figure: 2; Unit of that figure: Miles per US gallon
117.61 L/100 km; 2.4 UK mpg; 0.85 km/L; 50 US gallons per 100 miles
Why mpg and L/100 km do not move together
Mpg and km/L measure distance per unit of fuel, so a higher number is better. L/100 km measures fuel per distance, so a lower number is better. One is the reciprocal of the other, which means equal steps in mpg are not equal steps in fuel.
The chart shows it. Going from 10 to 15 US mpg cuts consumption from 23.52 to 15.68 L/100 km, a saving of 7.84 litres every 100 km. Going from 45 to 50 US mpg cuts it from 5.23 to 4.7, a saving of 0.53 litres. Both are a 5 mpg improvement, but the first saves about fifteen times as much fuel over the same distance.
That is why a consumption figure is the easier one to budget with: fuel for a trip is simply distance × L/100 km ÷ 100. If you think in mpg, the gallons per 100 miles results do the same job. 30 US mpg is 3.33 US gallons per 100 miles and 40 US mpg is 2.5.
Official figures are also measured on different test cycles in different countries, so converting the units of a US rating does not give the figure the same car would be rated at in Europe. The converter changes units only.
What this converter leaves out
- Electric vehicle units such as MPGe, kWh per 100 km and miles per kWh are not converted.
- It does not work out trip cost. Use the fuel cost calculator for distance and price.
- Results are rounded to two decimals, so converting a rounded result back can differ in the last digit: 30 UK mpg shows 24.98 US mpg, and 24.98 US mpg converts back to 30 UK mpg only after rounding.
- Zero and negative figures are rejected, because a reciprocal of zero has no meaning.
Step by step
- 1
Type your number in Fuel economy figure, for example 30.
- 2
Choose what it measures in Unit of that figure: Miles per US gallon, Miles per UK gallon, Litres per 100 km or Kilometres per litre.
- 3
Read the four results: Litres per 100 km, Miles per US gallon, Miles per UK gallon and Kilometres per litre.
- 4
Check Fuel used over 100 miles if you want gallons or litres per 100 miles.
- 5
Copy the Summary line, or use the table of nearby figures to compare cars.