Fuel Economy Converter
Convert fuel economy between litres per 100 km, km per litre and miles per gallon (US and UK).
Kilometres per litre
16.67 km/L
6 L/100 km
Litres per 100 km
6 L/100 km
Miles per gallon (US)
39.2 mpg (US)
Miles per gallon (UK)
47.1 mpg (UK)
Please note: The result is an estimate and has been rounded. Actual costs and values may differ, and no rights can be derived from this calculation.
How this number is calculated
The blocks use your input. Change a value above and they update with it.
Step 1 · Litres per 100 km
Step 2 · Kilometres per litre
Step 3 · Miles per gallon (US)
Step 4 · Miles per gallon (UK)
How the calculation works
This calculator converts a car's fuel economy. Enter the figure, pick its unit and you instantly see it in litres per 100 km, kilometres per litre and miles per gallon, in both US and UK (imperial) gallons.
Useful when you compare cars from different countries, or when you want to know what 30 mpg means in L/100 km. Want to know what a trip costs in fuel? Use the Fuel Cost Calculator in the same category; it uses the same conversion numbers.
The calculator first converts the figure to litres per 100 km. It then divides a fixed conversion number by that figure. For km/L the number is 100. For US mpg it is 100 × 3.785411784 ÷ 1.609344 ≈ 235.215, because a US gallon is 3.785411784 litres and a mile is 1.609344 km. For UK mpg it is 100 × 4.54609 ÷ 1.609344 ≈ 282.481, because a UK gallon is 4.54609 litres.
km/L and mpg are the inverse of L/100 km: the more efficient the car, the higher the number. That is why a value of 0 is not possible. Results are rounded to two decimals (L/100 km and km/L) or one decimal (mpg).
Formula
km/L = 100 ÷ L/100 km. mpg (US) = 235.215 ÷ L/100 km. mpg (UK) = 282.481 ÷ L/100 km.
Assumptions
- A US gallon is 3.785411784 litres, a UK (imperial) gallon 4.54609 litres and a mile 1.609344 km.
- The figure you enter is only converted, not checked or corrected for real-world driving.
- The type of fuel does not matter: petrol, diesel and LPG convert the same way.
- Electric consumption, such as kWh per 100 km, is not included.
- Results are rounded: L/100 km and km/L to two decimals, mpg to one decimal.
Example calculations
The button fills in the calculator above, so you can carry on from there.
-
Trip computer reading
Kilometres per litre
15.38 km/L
Fuel economy 6.5 L/100 km
-
American SUV
Kilometres per litre
10.63 km/L
Fuel economy 25 mpg (US)
-
British family car
Kilometres per litre
17.7 km/L
Fuel economy 50 mpg (UK)
Frequently asked questions
What is 30 mpg in L/100 km?
30 US mpg is 235.215 ÷ 30 = 7.84 L/100 km. 30 UK mpg is 282.481 ÷ 30 = 9.42 L/100 km.
How many mpg is 6 litres per 100 km?
6 L/100 km is 39.2 mpg in US gallons and 47.1 mpg in UK gallons. In kilometres per litre it is 16.67 km/L.
How do I convert km/L to L/100 km?
Divide 100 by the figure. 15 km/L is 100 ÷ 15 = 6.67 L/100 km, and the same sum turns 6.67 L/100 km back into 15 km/L.
Why are US and UK mpg different?
A UK (imperial) gallon is 4.546 litres and a US gallon is 3.785 litres. You drive further on a UK gallon, so the same car shows about 20% more mpg in UK gallons than in US gallons.
Is a higher or a lower number better?
For L/100 km, lower is better: you need less fuel for the same distance. For km/L and mpg, higher is better: you get further on the same amount of fuel.
Why don't I get the official fuel economy figure?
Official figures come from a standardised laboratory test, such as WLTP in Europe or the EPA test in the US. Real driving has different speeds, temperatures and driving styles, so real-world fuel use is often higher.
Sources and checks
Sources
- NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (opens in a new tab)
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement (opens in a new tab)
How we check it
This calculator has 19 fixed checks: 13 calculations with a result that is fixed in advance, and 6 cases of invalid input that must be rejected. They all run automatically every time we publish; if one fails, the calculator does not go live.
See the calculations
- Fuel economy 6 L/100 km → Kilometres per litre 16.67 km/L
- Fuel economy 15 km/L → Kilometres per litre 15 km/L
- Fuel economy 20 km/L → Kilometres per litre 20 km/L
- Fuel economy 30 mpg (US) → Kilometres per litre 12.75 km/L
- Fuel economy 40 mpg (UK) → Kilometres per litre 14.16 km/L
- Fuel economy 10 mpg (US) → Kilometres per litre 4.25 km/L
- Fuel economy 32 km/L → Kilometres per litre 32 km/L
- Fuel economy 0.5 L/100 km → Kilometres per litre 200 km/L
- Fuel economy 200 km/L → Kilometres per litre 200 km/L
- Fuel economy 60 L/100 km → Kilometres per litre 1.67 km/L
Changes
- : Sources added and content reviewed.
- : First version.
Last reviewed: · How we build and check our calculators
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