Updated October 2026
The formula
Miles per gallon and litres per 100 km are reciprocals with a constant in front. One measures how far a fixed amount of fuel takes you, the other how much fuel a fixed distance costs. So the conversion is a single division, and it runs in both directions.
L/100 km = 235.215 ÷ US MPG
L/100 km = 282.481 ÷ UK MPG
Swap the two sides to go back: US MPG = 235.215 ÷ L/100 km.
Where 235.215 comes from: 100 times the litres in a US gallon (3.785), divided by the kilometres in a mile (1.609). For the imperial gallon the litres become 4.546, which gives 282.481.
Worked through for a car rated at 30 US MPG:
- L/100 km: 235.215 ÷ 30 = 7.84 L/100 km
- UK MPG: 30 × 1.201 = 36.0 UK MPG
- km/L: 30 × 0.4251 = 12.75 km/L
The converter above keeps every decimal through the chain and only rounds what it shows you, so a figure converted there and back lands where it started.
Conversion tables
MPG to L/100 km, for the figures you see on most window stickers:
| US MPG | L/100 km | UK MPG | km/L |
|---|---|---|---|
| 15 | 15.68 | 18.0 | 6.38 |
| 20 | 11.76 | 24.0 | 8.50 |
| 25 | 9.41 | 30.0 | 10.63 |
| 30 | 7.84 | 36.0 | 12.75 |
| 35 | 6.72 | 42.0 | 14.88 |
| 40 | 5.88 | 48.0 | 17.01 |
| 50 | 4.70 | 60.0 | 21.26 |
And the other way, L/100 km to MPG, for Canadian, European and Australian figures:
| L/100 km | US MPG | UK MPG |
|---|---|---|
| 4 | 58.8 | 70.6 |
| 5 | 47.0 | 56.5 |
| 6 | 39.2 | 47.1 |
| 7 | 33.6 | 40.4 |
| 8 | 29.4 | 35.3 |
| 10 | 23.5 | 28.2 |
| 12 | 19.6 | 23.5 |
| 15 | 15.7 | 18.8 |
Why L/100 km is the more honest unit
MPG hides how much fuel you actually save. Researchers at Duke named it the MPG illusion in a 2008 paper in Science: people judge an upgrade by how many MPG it gains, when the fuel saved depends on where you start. Here is the same 10 MPG gain at two points on the scale, over 10,000 miles:
| Upgrade | Fuel before | Fuel after | Saved |
|---|---|---|---|
| 10 to 20 MPG | 1,000 gal | 500 gal | 500 gal |
| 30 to 40 MPG | 333 gal | 250 gal | 83 gal |
Same 10 MPG, six times the saving. In L/100 km the difference is obvious: the first upgrade drops from 23.5 to 11.8, the second from 7.8 to 5.9. Litres per distance is fuel per distance, which is what your wallet pays for. That is why swapping an old pickup for a slightly better pickup often saves more than swapping a sedan for a hybrid.
Which gallon is your figure in?
Get this wrong and every other step is pointless. The US gallon is 3.785 litres. The UK imperial gallon is 4.546 litres, 20 percent bigger. A British review that quotes 50 MPG is describing a car that does 41.6 MPG in American terms.
- US MPG: EPA stickers, fueleconomy.gov, American reviews and owner forums.
- UK MPG: British reviews, brochures and trip computers on UK cars.
- L/100 km: Canada (the EnerGuide label), Europe, Australia.
- km/L: Japan, India and most of Latin America. There is a separate MPG to km/L page for that one.
One more caveat. Converting units does not convert tests. An EPA rating and a European WLTP rating for the same car come from different driving cycles, so they will not match even after the arithmetic is right. The only figure that tells you what your car does is one you measured yourself, with the gas mileage calculator or a fill-up log.
Questions people actually ask
How do you convert MPG to L/100 km? +
How do I convert L/100 km back to MPG? +
Is 7 L/100 km good fuel economy? +
Why does a British car show a higher MPG than the same car in the US? +
Why is a lower L/100 km number better? +
Keep going
Gas mileage calculator
Stop converting someone else's number. Measure yours from two fill-ups.
Mileage reimbursement calculator
IRS 2026 rates, both halves of the year, and whether the check covers your gas.
Annual mileage calculator
Two odometer readings in, miles per year out, checked against your lease.