Fuel Economy Converter
Convert US and UK mpg, km/L and L/100 km — consumption figures use the correct reciprocal formula.
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How to use this tool
Steps for using the Unit Converter.
- Type a number into From — miles per US gallon are preselected. Commas and scientific notation such as 2.5e3 are accepted.
- Pick the units to convert between; the result in liters per 100 km (or whichever unit you choose) updates as you type. Use the swap button to reverse the conversion.
- Set the decimal places, turn on Show formula to see the calculation, and copy or share the result.
- Below the converter, the table lists every fuel economy unit with its exact definition, and the links open dedicated pages for the most common pairs.
Example
30 miles per US gallon to liters per 100 km
30 mpg (US)7.840486 L/100 km
Formula: L/100 km = 235.2145833 ÷ mpg (US)Common use cases
- Comparing car fuel figures between countries.
- Estimating fuel costs for a trip.
- Reading UK vs US vehicle reviews.
Fuel Economy unit table
| Unit | Symbol | System | Definition | In kilometers per liter |
|---|---|---|---|---|
| Kilometer per liter | km/L | Metric | Distance per litre of fuel | 1 |
| Liter per 100 km | L/100 km | Metric | Fuel used per 100 km (100 ÷ km/L) | 100 ÷ value |
| Mile per US gallon | mpg (US) | US customary | ≈ 0.425144 km/L | 0.4251437074 |
| Mile per imperial gallon | mpg (UK) | Imperial | ≈ 0.354006 km/L | 0.3540061899 |
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About fuel economy units
Fuel efficiency is expressed two opposite ways. Fuel economy — km/L and mpg — is distance per fuel: higher is better. Fuel consumption — L/100 km — is fuel per distance: lower is better. They're reciprocals, so converting needs division, not a single multiplier: L/100 km = 235.215 ÷ mpg (US).
US and UK mpg differ because the gallons differ: the imperial gallon is about 20% larger, so the same car gets about 20% more mpg in UK figures. 30 mpg (US) is 36 mpg (UK) and 7.84 L/100 km.
Limitations
- Zero can't be converted between economy and consumption units — the result would be infinite.
- Results are rounded for display only; the calculation keeps full precision (15 significant digits).
Frequently asked questions
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure (or 282.481 by UK mpg). 30 mpg (US) ≈ 7.84 L/100 km.
Why is UK mpg higher than US mpg for the same car?
An imperial gallon is 4.546 L and a US gallon 3.785 L, so a UK “mile per gallon” covers more fuel.
Is a lower L/100 km better?
Yes — it's the fuel used per 100 km, so lower means more efficient.
Are these fuel economy conversions exact?
Each unit is defined from its official definition (for example 1 inch = 2.54 cm exactly). Results are calculated in double precision and only rounded to the decimal places you choose when shown.