Fuel Economy Converter
Convert between MPG (US/UK), km/L and L/100km.
Results update as you type.
How it works
A fuel economy converter restates how efficiently a vehicle uses fuel in a different unit, moving between US miles per gallon, imperial UK miles per gallon, kilometres per litre and litres per 100 kilometres. Unlike simple unit conversions, this one is not a single multiply-and-divide, because some units measure distance per fuel (higher is better) while others measure fuel per distance (lower is better), so the converter inverts as well as rescales. This matters because fuel efficiency is quoted differently across the world, and the numbers are not comparable at a glance. The United States uses miles per gallon on a 3.785-litre gallon; the United Kingdom uses miles per gallon on a larger 4.546-litre imperial gallon, so a UK figure always looks better than the US figure for the same car; continental Europe uses litres per 100 kilometres, where a smaller number means a thriftier vehicle. Comparing a US-spec car against a European one, or reading an imported vehicle's brochure, demands a proper conversion. The converter pivots through litres per 100 kilometres, turning each distance-per-fuel input into that fuel-per-distance base and back out again. Because miles-per-gallon and km/L are inverse measures, a direct multiply would give nonsense; inverting through the shared base keeps every result correct. Buyers comparing models, drivers of imported cars, fleet managers and travellers renting abroad all rely on a fuel economy converter to judge running costs on one honest scale.
Convert through litres per 100 km, inverting distance-per-fuel units where needed
Distance-per-fuel units and fuel-per-distance units are inverses, so the converter first turns the input into litres per 100 km: from US mpg it computes 235.214583 divided by the value, from UK mpg 282.481 divided by the value, and from km/L 100 divided by the value. It then inverts that base figure into the target unit with the matching constant. A value of zero or below is rejected as NaN, since it would divide by zero or imply negative consumption.
Source:International System of Units (SI) — NIST
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter value, from and to.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Converted fuel economy updates instantly as you type — no button to press.
Frequently asked questions
Why is UK MPG higher than US MPG for the same car?
Because the imperial gallon used in the UK is about 4.546 litres, while the US gallon is about 3.785 litres — roughly twenty percent larger. Since a bigger gallon carries the car further, the same vehicle posts a higher miles-per-gallon number in imperial units. A car rated 30 US mpg is about 36 UK mpg. Always check which gallon a figure uses before comparing.
How do I convert MPG to L/100km?
Divide the constant 235.215 by the US miles-per-gallon figure to get litres per 100 kilometres, or divide 282.481 by the imperial UK figure. So 30 US mpg is about 7.84 L/100km. The relationship is inverse, not linear, because one unit measures distance per fuel and the other fuel per distance, which is why you divide a fixed constant rather than multiplying.
Is a lower L/100km better?
Yes. Litres per 100 kilometres measures how much fuel the car consumes to travel a set distance, so a smaller number means the car burns less fuel and is more efficient. This is the opposite of miles per gallon, where a higher number is better. A car at 5 L/100km is thriftier than one at 8 L/100km, using less fuel for the same journey.
What is a good fuel economy figure?
It depends on the vehicle class, but a modern efficient petrol car often achieves around 5 to 6 L/100km, roughly 40 to 47 US mpg or 47 to 56 UK mpg. Hybrids can reach 4 L/100km or better, while large trucks and SUVs may sit at 10 to 15 L/100km. Real-world figures vary with driving style, load, weather and traffic conditions.
Why can't I just multiply to convert fuel economy?
Because miles per gallon and litres per 100 km are reciprocal measures — one is distance divided by fuel, the other fuel divided by distance. Multiplying by a single factor would only rescale within the same type. Converting between them requires inverting the value through a shared base, which is why the converter divides a constant by your figure rather than scaling it directly, and rejects zero inputs.