Fuel Consumption converter

Fuel economy is measured in two opposite families, and this converter keeps both straight. Kilometer per liter (km/L) is this category's reference unit for the "distance per fuel" family, which also includes mile per gallon (US and UK), mile per liter, kilometer per gallon and nautical mile per liter — bigger numbers mean better efficiency. The second family, "fuel per distance," covers liter per 100 km, gallon (US) per 100 miles and liter per kilometer — here, smaller numbers mean better efficiency, the opposite direction.

Because the two families point in opposite directions, converting between them means dividing rather than multiplying. The featured pair, liter per 100 km to mile per gallon (US), is a reciprocal relationship: mpg (US) = 235.2145833 ÷ (L/100km). Converting within the same family — say, km/L to mpg (US) — is a normal ratio instead: multiply by 2.352145833.

A car rated at 8 L/100km converts to 235.2145833 ÷ 8 = 29.4 mpg (US). A more frugal car at 5 L/100km works out to 235.2145833 ÷ 5 = 47.0 mpg (US) — notice how a smaller L/100km number produces a larger mpg number, since the two scales run opposite ways.

Which family you'll see depends on where you are. Europe, most of Asia and most new-car spec sheets worldwide use liter per 100 km, because it answers the question drivers actually care about — how much fuel a trip will cost — in a way that scales linearly with distance. North America and, historically, the UK use miles per gallon instead, a holdover from imperial measurement that compares favorably when a car is already efficient but can be misleading when comparing two efficient cars, since mpg differences compress at the high end.

The most common error in this category is treating US and UK gallons as the same size. An imperial (UK) gallon holds about 4.546 liters, roughly 20% more than a US gallon's 3.785 liters, so a car advertised at 40 mpg in the UK is only about 33 mpg in US terms — the same physical fuel economy, just a different-sized bucket. Always check which gallon a figure is quoting before comparing it against a US rating.

A few units in this list are specialized rather than everyday. Nautical mile per liter appears in marine and aviation fuel planning, where distances are already tracked in nautical miles. Kilometer per gallon (US) is a hybrid that occasionally shows up when a metric-distance country still sells fuel by the gallon, letting a driver compare efficiency without converting the distance unit first.