Units explained
km/L vs L/100km explained
km/L measures distance per fuel unit. L/100km measures fuel per distance. They describe the same efficiency from opposite directions.
Use the reciprocal conversion
L/100km = 100 ÷ km/L, and km/L = 100 ÷ L/100km. A car doing 20 km/L consumes 5 L/100km. A car doing 10 km/L consumes 10 L/100km. Zero is not a valid input for either conversion.
Percent changes are not symmetric
Improving from 10 to 12 km/L is a 20% increase in distance per litre. Consumption falls from 10 to 8.333 L/100km, which is a 16.67% reduction. Fuel spending at the same distance and price falls by 16.67%, not 20%.
Compare cost using consumption
For a fixed annual distance, multiplying L/100km by distance ÷ 100 gives fuel volume directly. This makes consumption a convenient basis for budgeting. Economy units are equally valid, but use the reciprocal rather than subtracting MPG or km/L values to estimate savings.
Method and references
Examples use nominal geometry and fixed-price scenarios, with no vehicle-specific specifications implied. See our calculation methodology and editorial policy.
Unit reference: NIST Guide to the SI: conversion factors. Financial examples are arithmetic illustrations, not market-price forecasts.