Fuel Economy Converter
Convert fuel economy between US MPG, UK MPG, litres per 100 km and kilometres per litre, with a 30 MPG example and the US versus imperial gallon difference.
Results
Result
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Educational estimates · not financial advice · free, no signup
Formula / how it works
L/100 km = 235.215 ÷ MPG (US) = 282.481 ÷ MPG (UK). km/L = 100 ÷ (L/100 km). MPG (UK) = MPG (US) × 1.20095.
Detailed guide
What it is, how to use it, how to read the numbers, common mistakes, a worked example, formulas, and FAQs.
What this calculator is
Fuel economy is quoted in different ways around the world. The United States uses miles per US gallon, the UK uses miles per imperial gallon, much of Europe and Asia use litres per 100 kilometres, and some countries use kilometres per litre. This converter changes a rating between all four. Two traps matter. First, a UK gallon is about 20% larger than a US gallon, so the same car has a higher UK MPG figure. Second, L/100 km is a consumption figure where lower is better, while the other three are efficiency figures where higher is better. The conversions are reciprocal, not proportional.
When to use / who it helps
- You are comparing a car quoted in different units.
- You are reading a foreign car review.
- You are estimating the fuel for a road trip.
- You are checking the claims in an advertisement.
- You are moving between the US, UK and metric systems.
How to use
Steps
- Enter the value.
- Choose the unit you are converting from.
- Choose the target unit.
- Read the result.
- Check whether MPG is US or UK.
- Remember that for L/100 km a lower number is better.
How to interpret results
- Higher MPG and km/L are better; lower L/100 km is better.
- UK MPG is about 20% higher than US MPG for the same car.
- The conversion between MPG and L/100 km is a reciprocal.
- Official ratings differ from real-world use.
- Test cycles differ between regions.
Common mistakes & gotchas
- Comparing US MPG with UK MPG directly.
- Treating L/100 km as a higher-is-better figure.
- Using a proportional rather than reciprocal conversion.
- Comparing ratings from different test cycles.
- Rounding too early.
Worked example
Worked example — 30 MPG (US)
- L/100 km: 235.215 ÷ 30 = 7.84.
- km/L: 100 ÷ 7.84 ≈ 12.75.
- UK MPG: 30 × 1.20095 ≈ 36.03.
- Check: 282.481 ÷ 36.03 ≈ 7.84 L/100 km.
Result: 30 MPG (US) is 7.84 L/100 km, 12.75 km/L or about 36 MPG (UK).
To load the form's own demo values, tap Try example above the Calculate button.
How to calculate / formula
L/100 km = 235.215 ÷ MPG (US) = 282.481 ÷ MPG (UK). km/L = 100 ÷ (L/100 km). MPG (UK) = MPG (US) × 1.20095.
Frequently asked questions
How do I convert MPG to L/100 km?
Divide 235.215 by the MPG (US).
Why is UK MPG higher?
It uses the larger imperial gallon.
What is km/L?
Kilometres travelled per litre; higher is better.
Is L/100 km better when lower?
Yes, because it measures consumption.
Are official numbers realistic?
They are test values; real fuel use is often higher.
How is this different from the other fuel economy page?
The other page covers only US MPG and L/100 km; this one adds UK MPG and km/L.