MPG to L/100km: converting US fuel economy to the European standard
What this conversion does
It takes a fuel economy figure in US miles per gallon and restates it as litres per 100 kilometres, the unit used across Europe, China and most of Asia. The two describe the same physical efficiency but run in opposite directions: MPG counts the distance you get from a fixed amount of fuel, while L/100km counts the fuel you spend on a fixed distance.
Why the formula divides instead of multiplies
One US gallon is 3.785411784 litres and one mile is 1.609344 kilometres, so a car doing 1 MPG (US) covers 1.609344 km on 3.785411784 litres. Scaling that to a fixed 100 km gives an exact constant of 235.214583, which is the 235.2 in the formula. Because MPG sits in the denominator, this is a reciprocal relationship, not a proportional one: doubling your MPG halves your L/100km, but adding 10 MPG never subtracts a fixed number of litres.
MPG (US) to L/100km conversion table
Common US fuel economy figures with their metric equivalent. Note how the gaps narrow at the efficient end: 10 MPG costs you 23.5 litres per 100 km, but the step from 50 to 60 MPG saves barely 0.8 litres.
| Miles per gallon (US) | Litres per 100 km |
|---|---|
| 10 mpg | 23.5215 L/100km |
| 15 mpg | 15.6810 L/100km |
| 20 mpg | 11.7607 L/100km |
| 25 mpg | 9.4086 L/100km |
| 30 mpg | 7.8405 L/100km |
| 35 mpg | 6.7204 L/100km |
| 40 mpg | 5.8804 L/100km |
| 45 mpg | 5.2270 L/100km |
| 50 mpg | 4.7043 L/100km |
| 60 mpg | 3.9202 L/100km |
Reading the result the right way round
This is the single most common source of confusion when comparing cars across regions. In L/100km a lower number is better, because it states how much fuel the car burns; in MPG a higher number is better, because it states how far the car travels. A car advertised as "40" is efficient in America and thirsty in Germany, purely because the scales run opposite ways.
A quick mental check
Multiplying the two figures together always gives roughly 235, so you can sanity-check any result without a calculator: 30 MPG × 7.8 L/100km ≈ 235. This is why the hybrid and electric comparisons that quote "equivalent MPG" become misleading when converted — an efficiency of 100 MPG is only 2.35 L/100km, a number no petrol car of the same size reaches.
Frequently asked questions
Is this MPG figure for US or UK gallons?
Unqualified MPG on this site always means US gallons, matching the site's volume converter. A UK gallon is about 20% larger, so the same car reads roughly 1.20 times higher in imperial MPG — use the MPG (UK) tools if your figure came from Britain.
Why is 235.2 used in the formula?
It is 100 km divided by the distance one US gallon covers, derived from the exact definitions of the mile (1.609344 km) and the US gallon (3.785411784 L). The full value is 235.214583; the calculator uses the full precision and the formula line just rounds it for display.
Can I use this to compare a hybrid with a petrol car?
Yes, and it is often the clearest way to see the difference. A hybrid at 55 MPG works out to 4.28 L/100km against 7.84 L/100km for a 30 MPG petrol model — but remember that real-world MPG falls further short of the official figure on hybrids, so treat the comparison as a starting point.
What happens if I enter zero?
The tool refuses it. Zero miles per gallon would mean the car never moves on any amount of fuel, so the conversion goes to infinity and has no meaningful answer. Only positive values are accepted, and the same applies to negative or non-numeric input.
Why is my calculated figure slightly different from the car brochure?
Official figures come from a laboratory test cycle, not from the road. US EPA ratings and European WLTP ratings also use different cycles, so even a perfectly converted number will not match a real tank-to-tank measurement. Use the conversion to compare cars, not to predict your own fuel bill exactly.