Free tool

Gas mileage, any unit

Type a fuel-economy figure in any unit and every other unit updates instantly — UK MPG, US MPG, litres per 100 km and kilometres per litre.

L/100 km
MPG (UK)
MPG (US)
km/L

Edit any box — the other three recalculate. Figures are rounded for display; conversions use the exact gallon and mile definitions.

Quick reference: MPG (UK) to L/100km and km/L

MPG (UK)MPG (US)L/100kmkm/L
20 16.7 14.1 7.1
30 25.0 9.4 10.6
40 33.3 7.1 14.2
50 41.6 5.6 17.7
60 50.0 4.7 21.2

Why two different MPG?

The UK and US both use “miles per gallon”, but the gallon isn’t the same size. A UK (imperial) gallon is 4.546 litres; a US gallon is 3.785 litres. The same car therefore reads about 20% higher in UK MPG than US MPG — a frequent source of confusion when comparing cars across the Atlantic. L/100km avoids the problem entirely, which is why most of the world uses it.

Putting a figure into real money? Drop your converted economy into the fuel cost calculator to see what a trip costs.

Frequently asked questions

How do you convert MPG to L/100km?
They are inversely related. For UK gallons: L/100km = 282.48 ÷ MPG. For US gallons: L/100km = 235.21 ÷ MPG. So 40 MPG (UK) ≈ 7.1 L/100km, while 40 MPG (US) ≈ 5.9 L/100km.
What’s the difference between UK and US MPG?
The gallon is different. A UK (imperial) gallon is 4.546 litres; a US gallon is only 3.785 litres. Because the US gallon is smaller, the same car shows a lower MPG figure in the US than in the UK — about 20% lower. Always check which gallon a figure uses.
Is a higher or lower number better?
For MPG and km/L, higher is better — you travel further per unit of fuel. For L/100km it’s the opposite: lower is better, because you’re burning fewer litres to cover the same distance.
What is good fuel economy?
As a rough guide, 50+ MPG (UK) / ~5.6 L/100km is very economical, 40 MPG (UK) / ~7 L/100km is solid for a family car, and under 25 MPG (UK) / over ~11 L/100km is thirsty. Hybrids and small diesels sit at the efficient end.
The CheapGas app

The cheapest pump, before you leave the house.

Everything on this site plus price-drop alerts, saved stations on your routes, and a fill-up log that shows your real cost per mile over time.

Coming soon