Fuel Economy Converter: MPG, km/L and L/100 km
Convert fuel economy between MPG (US), MPG (UK), km/L, L/100 km, mi/L and km/gal. See every unit at once, the inverse L/100 km formula and a table of common values.
30 MPG (US) = 7.84049 L/100 km
- MPG (US)
- 30
- MPG (UK)
- 36.0285
- km/L
- 12.7543
- L/100 km
- 7.84049
- mi/L
- 7.92516
- km/gal (US)
- 48.2803
Higher MPG, km/L and mi/L mean a more efficient car; a lower L/100 km means the same. L/100 km = 235.214583 ÷ MPG (US).
About the Fuel Economy Converter
The Fuel Economy Converter turns a fuel economy figure into the other common units. Type a number, choose the unit you have and the unit you want, and the answer appears as you type. Below the main answer the page lists the same figure in all six units at once: miles per gallon (US), miles per gallon (UK), kilometres per litre, litres per 100 km, miles per litre and kilometres per gallon (US).
Fuel economy is written two opposite ways around the world. The United States quotes distance per volume, miles per US gallon, so a bigger number is better. Most of Europe, Canada and Australia quote volume per distance, litres per 100 km, so a smaller number is better. The United Kingdom quotes miles per imperial gallon, which is about 20% larger than a US gallon, so a car rated 30 MPG (UK) is a 25 MPG (US) car. This page keeps all three straight.
How to use the converter
Steps
- Type your fuel economy into Fuel economy, for example 30.
- Pick the unit you have under From and the unit you want under To. The swap button exchanges them.
- Read the headline result, or scan the tiles to see the same figure in every unit.
- Zero, negative numbers and text are explained in a message instead of giving a wrong answer.
The formulas
Every unit is tied together by three exact definitions: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 litres and 1 imperial (UK) gallon = 4.54609 litres.
Because MPG and L/100 km are reciprocals, the relationship is not a simple multiplication. Doubling the MPG halves the L/100 km. The same 235.214583 constant works in both directions: MPG (US) = 235.214583 / (L/100 km).
Worked examples
Example 1: MPG to L/100 km
A car that returns 30 MPG (US) uses 235.214583 / 30 = 7.84049 litres per 100 km. The same car is 12.7543 km/L.
Example 2: L/100 km to MPG
A European hatchback rated 6 L/100 km does 235.214583 / 6 = 39.2024 MPG (US), or 47.0802 MPG (UK).
Example 3: US to UK miles per gallon
An imperial gallon holds 4.54609 / 3.785411784 = 1.20095 US gallons, so a UK MPG figure is multiplied by 0.832674 to get the US figure. 30 MPG (UK) is 24.9802 MPG (US).
MPG (US) to L/100 km table
| MPG (US) | L/100 km |
|---|---|
| 10 | 23.521 |
| 15 | 15.681 |
| 20 | 11.761 |
| 25 | 9.409 |
| 30 | 7.840 |
| 35 | 6.720 |
| 40 | 5.880 |
| 45 | 5.227 |
| 50 | 4.704 |
| 60 | 3.920 |
L/100 km to MPG (US) table
| L/100 km | MPG (US) |
|---|---|
| 3 | 78.405 |
| 4 | 58.804 |
| 5 | 47.043 |
| 6 | 39.202 |
| 7 | 33.602 |
| 8 | 29.402 |
| 9 | 26.135 |
| 10 | 23.521 |
| 12 | 19.601 |
| 15 | 15.681 |
Why MPG can mislead
Because MPG is a reciprocal scale, equal MPG gains save very different amounts of fuel. Going from 10 to 20 MPG saves 11.8 litres per 100 km, while going from 40 to 50 MPG saves only 1.2 litres per 100 km. If you are comparing cars by running cost, L/100 km compares fairly: a car that uses 2 litres less per 100 km saves the same fuel whatever it started at.
Privacy
Nothing is uploaded; every calculation runs in your browser and never leaves your device. The page keeps no history and needs no account.
Related tools
Convert the units behind these figures with the Volume Converter for gallons and litres or the Length Converter for miles and kilometres. The Speed Converter handles mph and km/h, and the Unit Price Calculator compares prices per litre or per gallon.
Frequently asked questions
How do I convert MPG to L/100 km?
Divide 235.214583 by the MPG figure when it is in US gallons. 30 MPG (US) is 235.214583 / 30 = 7.84049 L/100 km. For imperial (UK) gallons divide 282.480936 by the MPG figure instead. The same constants work in the other direction to turn L/100 km into MPG.
Why do MPG and L/100 km run in opposite directions?
MPG measures distance per fuel, so a bigger number means a thriftier car. L/100 km measures fuel per distance, so a smaller number means a thriftier car. The two scales are reciprocals: doubling the MPG halves the L/100 km.
What is the difference between MPG (US) and MPG (UK)?
The gallons are different sizes. A US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, about 20% larger. The same car therefore has a bigger MPG (UK) number than MPG (US): 30 MPG (UK) is 24.98 MPG (US), and 30 MPG (US) is 36.03 MPG (UK).
How do I convert km/L to MPG?
Multiply km/L by 2.352146 for MPG (US) or by 2.824809 for MPG (UK). For example 12 km/L is 28.23 MPG (US). To go back, multiply MPG (US) by 0.425144 to get km/L.
Which constants does the converter use?
One mile is exactly 1.609344 km, one US gallon is exactly 3.785411784 litres and one imperial gallon is exactly 4.54609 litres. Every unit is converted through kilometres per litre, so a round trip returns the number you started with.
Why does it refuse zero?
A car cannot cover any distance on zero MPG, and zero L/100 km would mean no fuel is burned. Converting such a value would give an infinite answer in the other unit, so the page asks for a number greater than zero instead.
How many digits does the result show?
Results are shown to six significant digits with no trailing zeros, such as 7.84049 L/100 km. The conversion tables on the page show three decimal places.