Fuel economy is quoted four different ways depending on where the car was sold, and two of them run in opposite directions. Comparing a US review against a European one without converting produces confident nonsense.
What the Fuel Economy Converter does
Converts between MPG (US), MPG (UK), L/100km and km/L.
US and UK MPG are not the same figure, because the gallons differ: 30 MPG US is about 36 MPG UK for exactly the same car. That gap alone explains many baffling car-forum arguments.
Open the Fuel Economy Converter and follow the settings and checks below.
The four units
| Setting | What it means |
|---|---|
| MPG (US) | Miles per US gallon — 3.785 L |
| MPG (UK) | Miles per UK gallon — 4.546 L |
| Same car | 30 MPG US ≈ 36 MPG UK |
| L/100km | Litres per 100 km — lower is better |
| km/L | Kilometres per litre — higher is better |
| MPG and km/L | Distance per fuel — higher is better |
| L/100km | Fuel per distance — inverted |
| Conversion | Not linear between the two conventions |
How to use it
- Enter the figure and say which unit it is in.
- Read every other unit.
- Check which MPG a source means before comparing — it often does not say.
Practical advice
When a car review quotes MPG, find out whose gallon it means. A US publication quoting 30 MPG and a UK one quoting 36 MPG may be describing the identical car, and someone comparing the two numbers concludes the second is 20% more efficient. This is the commonest error in cross-border car comparisons.
Common questions
Why are US and UK MPG different?
Because the gallon is. A US gallon is 3.785 litres, a UK gallon 4.546 — about 20% larger — so the same car travels further on one UK gallon. Same efficiency, different number.
Why is L/100km inverted?
It measures fuel consumed per fixed distance rather than distance per fixed fuel, so a smaller figure means less fuel. It is arguably the more useful convention for budgeting, since fuel is what you buy.
Is the conversion a simple multiplication?
Between MPG and km/L, yes. Between either of those and L/100km, no — it is a reciprocal relationship, which is why you cannot convert by scaling and why halving one does not halve the other.
Which unit should I use?
Whichever your region uses, so your figures match the prices and reviews around you. When comparing across regions, convert first — every time.
Useful next tools
- Fuel Cost Calculator — Trip fuel cost from distance, economy and fuel price.
- Unit Converter — Length, mass, temperature, area, volume, speed and data.
- Volume Converter — Convert litres, gallons, cups, pints and millilitres.
- Mileage Reimbursement — Work out mileage reimbursement from distance and rate.
- Travel Time Calculator — How long a trip takes from distance and average speed.
- Length Converter — Convert miles, km, feet, inches, metres and more.
Vootkit provides a planning estimate, not a guaranteed fare, reimbursement, journey time or statement of local custom. Prices, traffic, exchange rates, employer rules and destination guidance can change; verify important figures with the relevant provider or authority.
Try the tools from this guide
Keep reading
How to Estimate Travel Time from Distance and Speed
Calculates travel time from a distance and an average speed, in kilometres or miles.
How to Calculate the Fuel Cost of a Journey
Multiplies distance by consumption by price. Handles both conventions — L/100km (lower is better) and MPG (higher is better) — which is the detail that…
How to Calculate Mileage Reimbursement Correctly
Multiplies distance by a per-unit rate. Defaults to 0.67, which reflects a recent published business rate.