Fuel Economy Converter (MPG, L/100km, km/L)
Convert fuel economy between US MPG, Imperial MPG, litres per 100 km and kilometres per litre. Enter a value in any unit and see all the others instantly.
How to use
- Enter a fuel-economy value.
- Pick the unit it is given in.
- Read the equivalent in the other three units; the input unit is highlighted.
- Try 30 MPG (US) — it is about 7.84 L/100km and 12.75 km/L.
About this tool
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Fuel economy is measured differently around the world: the US uses miles per gallon (US gallon), the UK uses miles per gallon (Imperial gallon), most of Europe uses litres per 100 km, and many other countries use kilometres per litre. Because L/100km measures consumption (lower is better) while the others measure distance per fuel (higher is better), converting between them is not a simple multiplication — it involves reciprocals. This tool handles all of that: enter a value in any one unit and it instantly shows the equivalent in the other three, using the exact gallon and mile definitions (1 US gallon = 3.785411784 L, 1 Imperial gallon = 4.54609 L, 1 mile = 1.609344 km). Everything runs locally in your browser — nothing is uploaded.
Frequently asked questions
Why isn't US MPG the same as Imperial MPG?
The two use different gallons. A US gallon is 3.785 L while an Imperial (UK) gallon is 4.546 L — about 20% larger — so the same car shows a higher number in Imperial MPG than in US MPG.
Why is converting to L/100km not just a fixed multiplier?
MPG and km/L are 'distance per fuel' (more is better) while L/100km is 'fuel per distance' (less is better). They are inversely related, so the conversion uses a division: L/100km = 235.215 ÷ MPG(US), for example.
Which gallon and mile values are used?
Exact international definitions: 1 US gallon = 3.785411784 L, 1 Imperial gallon = 4.54609 L, 1 mile = 1.609344 km. Results are rounded to four decimal places.
Why do savings from a small efficiency gain look bigger than expected?
Because miles per gallon is a reciprocal scale, so equal steps in it are not equal savings. Going from 10 to 15 mpg saves more fuel over the same distance than going from 30 to 40, which is why fuel used per distance — litres per 100 km — is the more honest number when comparing vehicles or costing a change. Judge upgrades by fuel per distance, not by the headline figure.
Why does my car's computer disagree with what I calculate at the pump?
Because it is estimating from injector timing and inferred load rather than measuring what left the tank, and estimates are commonly a few per cent optimistic. Tank-to-tank arithmetic has its own error — pump cut-off varies with the nozzle, the angle and how full you fill — so a single tank means little. Average several fills to get a figure worth comparing.
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