Litres per 100 kilometres measures fuel used for a fixed distance. Miles per gallon measures distance travelled for a fixed volume. Because one rises while the other falls, converting between them requires a reciprocal formula.
The two MPG standards
A US liquid gallon is smaller than an Imperial gallon. The same vehicle therefore has a lower numeric US MPG than Imperial MPG. Never use an MPG value until its gallon standard is known.
| Measure | Conversion from L/100 km |
|---|---|
| US MPG | 235.214583 ÷ L/100 km |
| Imperial MPG | 282.480936 ÷ L/100 km |
| km/L | 100 ÷ L/100 km |
Worked Canadian example
For 8 L/100 km, divide each constant by 8. The result is about 29.402 US MPG or 35.310 Imperial MPG. The consumption is also 12.5 km/L.
Convert MPG back to L/100 km
The same constants work in reverse because the relationship is reciprocal. Divide 235.214583 by US MPG, or 282.480936 by Imperial MPG.
40 US MPG = 235.214583 ÷ 40 ≈ 5.880 L/100 kmEstimate litres for a trip
Multiply trip kilometres by L/100 km, then divide by 100. At 8 L/100 km, a 500 km trip uses an estimated 40 litres.
Trip litres = distance in km × L/100 km ÷ 100Why actual fuel use differs
- Speed, acceleration, traffic, and route
- Temperature, wind, and road conditions
- Vehicle load, tires, maintenance, and accessories
- Laboratory rating method versus real operation