L/100 km to MPG: compare fuel economy and annual running cost
Convert US and imperial MPG correctly, estimate fuel bills and combine real driving records without averaging ratios incorrectly.
Check which gallon the figure uses
MPG means miles per gallon, but a US gallon and an imperial gallon are different sizes. For the same vehicle, imperial MPG is numerically higher. Approximate conversions are US MPG = 235.215 ÷ L/100 km and imperial MPG = 282.481 ÷ L/100 km. Use the fuel economy converter and choose the correct gallon system.
Work through an 8 L/100 km example
A vehicle consuming 8 L/100 km achieves approximately 29.4 US MPG or 35.3 imperial MPG. Lower L/100 km means less fuel used, whereas higher MPG means greater distance per gallon. These are reciprocal measures: doubling MPG halves consumption for the same distance. The NIST unit tables distinguish the gallon definitions.
Turn consumption into a budget
At 15,000 km per year and 8 L/100 km, fuel use is 15,000 × 8 ÷ 100 = 1,200 litres. At an assumed 2 currency units per litre, annual fuel cost is 2,400. A reduction to 6 L/100 km would save 300 litres, or 600 at the same price. Enter your own tariff in the fuel cost calculator; these example prices are not live quotes.
Combine journeys using totals
Do not simply average dashboard ratios when trip distances differ. If one trip uses 8 litres over 100 km and another uses 18 over 300 km, combined consumption is 26 ÷ 400 × 100 = 6.5 L/100 km. Use consistent refill measurements and several tanks to reduce pump and traffic variation.
Compare ownership costs fairly
Test-cycle figures are useful reference points, not promises for your roads, speed or air-conditioning load. Add insurance, servicing, depreciation and finance before choosing a vehicle based on fuel alone. For an EV comparison, read how charging cost is calculated and keep annual distance and energy-price assumptions consistent.