Fuel economy converter
Convert between miles per gallon, litres per 100 km and kilometres per litre. Why the conversion is a division, not a multiplication.
Runs in your browser
Every fuel economy unit, one page
Pick any two units above. The conversions people look up most often have dedicated pages with reference tables, linked below.
This category is not linear
Every other converter on this site multiplies. This one divides, because the units measure opposite things:
| Unit | Measures | Bigger is |
|---|---|---|
| Litres per 100 km | consumption | worse |
| Miles per gallon | economy | better |
| Kilometres per litre | economy | better |
There is no factor between mpg and L/100 km. There is only:
L/100km = 235.2146 ÷ mpg (US)
L/100km = 282.4809 ÷ mpg (imperial)
L/100km = 100 ÷ km/LEach of those constants is its own inverse: dividing 235.2146 by an mpg figure gives L/100 km, and dividing it by a L/100 km figure gives mpg back. The same division works in both directions.
Which gallon
The two mpg figures are 20% apart, because the two gallons are:
| Litres | 30 mpg equals | |
|---|---|---|
| US gallon | 3.785 | 7.84 L/100km |
| Imperial gallon | 4.546 | 9.42 L/100km |
A British car advertised at 48 mpg is a US 40 mpg car. Neither figure is wrong. This
converter’s mpg is the US gallon unless the imperial unit is chosen.
The MPG illusion
Because the relationship is reciprocal, equal-looking improvements save wildly unequal amounts of fuel. This is the single most useful thing on this page.
Over 10,000 km:
| Change | L/100km | Fuel saved per 10,000 km |
|---|---|---|
| 10 → 20 mpg | 23.52 → 11.76 | 1176 L |
| 20 → 30 mpg | 11.76 → 7.84 | 392 L |
| 30 → 40 mpg | 7.84 → 5.88 | 196 L |
| 40 → 50 mpg | 5.88 → 4.70 | 118 L |
| 50 → 60 mpg | 4.70 → 3.92 | 78 L |
Replacing a 10 mpg truck with a 20 mpg one saves fifteen times as much fuel as replacing a 50 mpg car with a 60 mpg one, despite both being a ten-mpg improvement. Doubling from 10 to 20 saves three times as much as doubling from 30 to 60.
This is invisible in mpg and obvious in L/100 km, which is the argument for the metric unit: consumption is what you actually pay for, and it is linear.
Reference figures
| L/100km | mpg (US) | mpg (UK) | km/L | |
|---|---|---|---|---|
| Large SUV | 14.0 | 16.8 | 20.2 | 7.1 |
| Family petrol car | 8.0 | 29.4 | 35.3 | 12.5 |
| Small petrol car | 6.0 | 39.2 | 47.1 | 16.7 |
| Diesel hatchback | 4.5 | 52.3 | 62.8 | 22.2 |
| Hybrid | 4.0 | 58.8 | 70.6 | 25.0 |
| Efficient hybrid | 3.5 | 67.2 | 80.7 | 28.6 |
Electric cars use a different unit entirely
An EV has no gallons, so consumption is quoted in kWh per 100 km — or, in the US, in MPGe, which converts electricity into a notional gallon of petrol at 33.7 kWh per gallon.
| kWh/100km | MPGe | |
|---|---|---|
| Efficient EV | 15 | 149 |
| Typical EV | 18 | 124 |
| Large EV | 22 | 102 |
MPGe is not comparable to mpg in any physical sense; it is a labelling device. See the energy converter for what a kWh actually is.
Where people go wrong
km/L is not L/100 km divided by 100. It is 100 divided by it. 10 km/L is 10 L/100 km only by coincidence — the two curves cross at exactly that point and nowhere else.
A test figure is not a real one. WLTP, EPA and the older NEDC cycles produce different numbers for the same car, and all of them are optimistic against ordinary driving.