Fuel Economy Calculator
Work out your real fuel economy from the fuel you added and the distance driven
Loading the tool…
Calculates your car's real fuel economy from the fuel added and the distance driven, in km/L, L/100 km, US mpg and UK mpg, and keeps a log of fill-ups with your average.
How to use
- Choose the "Fuel unit" and enter the "Fuel added" from the pump receipt.
- Under "Distance from", choose "Odometer readings" and enter the "Odometer at the previous fill-up" and the "Odometer now", or enter the "Distance driven" directly.
- Optionally enter the "Amount paid" and pick how to "Show fuel economy as".
- Press "Save this fill-up" to add it to the "Fill-up log" with the "Average fuel economy" and a chart.
How it works
- km/L = distance ÷ fuel added, and L/100 km = fuel added ÷ distance × 100. The average is total distance ÷ total fuel, not an average of the separate results.
- For an accurate figure, fill the tank to full, note the odometer, and fill to full again next time. The fuel added then equals the fuel used.
- One mile is 1.609344 km, a US gallon is 3.785411784 L and a UK gallon is 4.54609 L.
- The log is saved on this device and can be downloaded with "Save as CSV".
Questions and answers
- How do I calculate my real fuel economy?
- After a full tank, divide the distance driven by the fuel needed to fill the tank again. 520 km on 40 L is 520 ÷ 40 = 13 km/L.
- How do I convert km/L to L/100 km?
- Divide 100 by the km/L value. 13 km/L is 100 ÷ 13 ≈ 7.69 L/100 km.
- How do I convert mpg to km/L or L/100 km?
- Multiply US mpg by 0.4251 to get km/L, or divide 235.21 by it to get L/100 km. 30 mpg (US) is about 12.75 km/L or 7.84 L/100 km. For UK mpg, use 0.354 and 282.48.
- Is the result wrong if I do not fill the tank to full?
- The fuel added then differs from the fuel used, so single results can vary a lot. Saving many fill-ups brings the average closer to the real figure.