Fuel Consumption Calculator
The formula
Consumption (L/100 km) = fuel used (litres) ÷ distance (km) × 100
Example: 45 litres for 620 km gives 45 ÷ 620 × 100 = 7.26 L/100 km. 30 litres for 500 km gives 6.0 L/100 km.
Unlike miles per gallon, a lower figure means a more economical vehicle.
Measuring it accurately: the full-tank method
- Fill the tank completely and reset the trip counter.
- Drive normally until the tank is at least half empty.
- Fill it completely again at the same station if possible, and note the litres added.
- Divide those litres by the distance shown on the trip counter, then multiply by 100.
Repeat over several tanks for a reliable average: on-board computers are often a few percent optimistic.
Converting to miles per gallon
| L/100 km | US mpg | UK mpg |
|---|---|---|
| 4 | 58.8 | 70.6 |
| 5 | 47.0 | 56.5 |
| 6 | 39.2 | 47.1 |
| 7.26 | 32.4 | 38.9 |
| 8 | 29.4 | 35.3 |
| 10 | 23.5 | 28.2 |
Formulas: US mpg = 235.21 ÷ L/100 km; UK mpg = 282.48 ÷ L/100 km (the UK gallon is larger).
Cost of a trip
Cost = distance ÷ 100 × consumption × price per litre. A 400 km trip at 7.26 L/100 km with fuel at €1.80 a litre costs 4 × 7.26 × 1.80 ≈ €52, or €0.13 per kilometre — before wear, tolls and insurance.
What raises consumption
- Speed: air resistance rises with the square of speed. Driving at 110 instead of 130 km/h on the motorway typically saves 10–20% of fuel.
- Short trips and cold engines, frequent stops, aggressive acceleration.
- Under-inflated tyres (check them monthly), roof boxes, extra weight, air conditioning.
Typical modern cars use 5–8 L/100 km of petrol or 4–6.5 L of diesel in mixed driving; official figures (WLTP) are measured in standard conditions and are often exceeded in real life. Use the volume converter for gallons and the speed calculator for travel times.
Frequently Asked Questions
How do I convert L/100 km to mpg?
Divide 235.21 by the L/100 km figure for US mpg, or 282.48 for UK mpg. 7 L/100 km ≈ 33.6 US mpg or 40.4 UK mpg.
Why is my real consumption higher than the official figure?
Official WLTP figures are measured on a standard test cycle. Speed, traffic, temperature, load and driving style usually push real consumption 10–30% higher.
How do I calculate the cost per kilometre?
Multiply your consumption by the fuel price and divide by 100. At 6 L/100 km and €1.80 a litre: 6 × 1.80 ÷ 100 = €0.108 per km.