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Convert between mpg and L/100km — the world's two fuel-economy systems.
Convert fuel economy between miles per gallon (US) and liters per 100 km — the two systems the world actually uses. Remember: with mpg, higher is better; with L/100km, lower is better.
Fuel economy is measured in two philosophically opposite ways. The U.S. uses miles per gallon (mpg), where bigger is better. Most of the world uses liters per 100 kilometers (L/100km), where smaller is better. The UK uses miles per imperial gallon, which is about 20 percent larger than the U.S. gallon — so 40 imperial mpg is only 33.3 U.S. mpg, a comparison trap for transatlantic car shoppers. Converting between mpg and L/100km is a reciprocal relationship: L/100km = 235.21458 / mpg (U.S.), and mpg (U.S.) = 235.21458 / L/100km. For imperial mpg, the constant is 282.481.
Why the reciprocal matters: fuel savings are not linear in mpg. Going from 15 to 20 mpg saves far more fuel than going from 40 to 45 mpg, because each additional mpg represents a smaller slice of consumption. The L/100km scale is linear in fuel used, which makes it the honest scale for comparing costs: a car at 5 L/100km always uses exactly half the fuel of one at 10 L/100km, while 60 mpg is not 'twice as good' as 30 mpg in any linear sense — well, actually it is exactly twice the distance per gallon, but the gallons saved per year diminish. For budget math, convert to L/100km (or gallons per 100 miles) first.
To estimate annual fuel cost from economy: divide annual distance by the economy figure in matching units, then multiply by fuel price. A car driven 15,000 km/year at 7.5 L/100km burns 15,000/100 x 7.5 = 1,125 liters per year; at $1.50/L that is $1,687.50. This calculator converts between mpg (U.S. and imperial), L/100km, and km/L.
The two scales are inverses linked by a constant: L/100km = 235.214583 ÷ mpg, and mpg = 235.214583 ÷ (L/100km). Note the scales run in opposite directions — efficient cars have high mpg and low L/100km.
Divide the constant: 235.21458 / 30 = 7.8405, rounded to 7.84 L/100km. Reverse check: 235.21458 / 7.8405 = 30.0 mpg, confirming the reciprocal. For a European buyer, 7.84 L/100km reads as a moderately efficient gasoline car — typical family hatchbacks sit between 6 and 8. Note the imperial trap: 30 imperial mpg would be 282.481 / 30 = 9.42 L/100km, a thirstier car than the American 30 mpg suggests.
Divide the constant by the consumption: 235.21458 / 6.5 = 36.1869, rounded to 36.2 mpg (U.S.). That is an efficient hybrid or diesel figure. Annual fuel check: at 20,000 km/year, consumption is 20,000/100 x 6.5 = 1,300 liters; at $1.60/L, the yearly fuel bill is $2,080. Compare a 9.0 L/100km SUV over the same distance: 1,800 liters, or $2,880 — the 2.5 L/100km gap is worth $800 a year, the kind of concrete number this conversion exists to produce.
About 7.84 L/100km. Enter 30, choose mpg → L/100km — the formula is 235.214583 ÷ 30.
No — they run in opposite directions. High mpg means efficient; high L/100km means thirsty. Both describe the same car, just from different angles.
Yes — US and imperial gallons differ (1 imperial gallon = 1.20095 US gallons). This converter uses US gallons, the standard for American mpg figures.