⛽ Fuel Economy
Convert fuel efficiency between km/L, MPG and L/100km free. Handles the inverse relationship correctly, US and UK gallons.
⛽ Fuel Economy
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About the Fuel Economy Tool
Fuel economy conversion is more subtle than most unit conversions because two of the common units run in opposite directions. Kilometres per litre and miles per gallon measure distance per fuel — higher is better. Litres per 100 kilometres measures fuel per distance — lower is better.
Converting between them requires taking a reciprocal, not just multiplying by a factor, which is why simple conversion attempts often produce nonsense. Add the US and imperial gallon distinction and the arithmetic gets genuinely error-prone. This converter handles all of it correctly in your browser.
How to Use Fuel Economy
- Enter your fuel economy figure.
- Select the source unit, noting whether MPG is US or imperial.
- Select the target unit.
- Read the correctly converted result.
When to Use This Tool
- Comparing vehicle efficiency figures quoted in different markets
- Converting a car’s stated mileage into a familiar unit
- Understanding European L/100km ratings from a US perspective
- Calculating fuel costs for a journey using foreign specifications
- Comparing your measured economy against manufacturer claims
Things Worth Knowing
- L/100km is inversely related to km/L and MPG — lower values mean better efficiency.
- US MPG and imperial MPG differ by about 20%, because the gallons differ.
- To convert km/L to L/100km, divide 100 by the km/L figure.
Quick Facts
| Tool name | Fuel Economy |
| Category | Unit Converters |
| Price | Free — no account, no trial, no watermark |
| Where it runs | Entirely in your browser (client-side) |
| Files uploaded | None — your data never leaves your device |
| File size limit | None imposed; limited only by device memory |
| Works offline | Yes, once the page has loaded |
| Platforms | Windows, macOS, Linux, Android, iOS |
Frequently Asked Questions
Why is L/100km lower for a more efficient car?
Because it measures fuel consumed per distance rather than distance per fuel. Using less fuel to travel 100 km is better, so a smaller number indicates better efficiency — the opposite of MPG.
How do I convert km/L to L/100km?
Divide 100 by the km/L value. A car achieving 20 km/L uses 100 ÷ 20 = 5 L/100km. The relationship is reciprocal, not proportional.
What is the difference between US and UK MPG?
The gallon. A UK imperial gallon is 4.546 litres against the US gallon’s 3.785, so the same car rates about 20% higher in imperial MPG. Always check which is quoted.
Why do real-world figures differ from official ratings?
Official figures come from standardised test cycles that do not reflect typical driving. Traffic, air conditioning, terrain, tyre pressure, and driving style all reduce real economy below the rated figure.