Global Fuel CalculatorHow to calculate fuel consumption
Working out your fuel consumption takes two numbers and one division. Once you know the method, you can calculate petrol usage, estimate gasoline for a trip, or check whether a car is drinking more than it should.
The formulas
- Litres per 100 km = litres used ÷ kilometres driven × 100
- Kilometres per litre = kilometres driven ÷ litres used
- Miles per gallon = miles driven ÷ gallons used (US or imperial, never mixed)
Worked examples
- Metric: 42 litres over 520 km is 42 ÷ 520 × 100 = 8.08 L/100km, or 12.38 km/L.
- US: 312 miles on 11.4 US gallons is 27.37 MPG, which is 8.59 L/100km.
- UK: 420 miles on 45 litres is 9.90 imperial gallons, so 42.43 MPG (6.66 L/100km). UK drivers buy litres, so convert to imperial gallons first (litres ÷ 4.54609).
A fuel consumption estimate for any trip
Once you know your consumption, estimating fuel for a journey is multiplication: distance × L/100km ÷ 100. A 450 km trip at 8 L/100km needs 36 litres. In miles and gallons, divide the distance by your MPG. Add a margin of around 10% for a loaded car, motorway speeds or hilly roads.
How to calculate fuel consumption
- Fill the tank. Fill to the automatic cut-off and note the odometer or reset the trip meter.
- Drive normally. Use the car as usual until the tank is at least half empty, ideally a few hundred kilometres.
- Refill. Fill to the same cut-off at the same pump and write down the litres or gallons added.
- Divide. Divide the fuel used by the distance. For L/100km, multiply the result by 100.
- Cross-check. Enter both figures into the fuel consumption calculator to confirm the result in every unit.
Common questions
How do I calculate petrol usage per kilometre?
Divide the litres you used by the kilometres you drove. 40 litres over 500 km is 0.08 litres per kilometre, which is the same as 8 L/100km.
Can I work out gasoline use without a calculator?
Yes. Divide fuel by distance with any basic calculator or by hand. The fuel consumption calculator just does it for every unit at once and avoids gallon mix-ups.
What is the difference between fuel consumption and fuel economy?
Consumption is fuel per distance, so lower is better. Economy is distance per fuel, so higher is better. They are reciprocals of each other.