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Fuel Cost Calculator

Fuel economy is quoted four different ways around the world, and a US gallon is about 20% smaller than an imperial one. Every unit here is an explicit choice, so the answer matches whatever your car's display and your local pump actually use.

Number of people sharing the cost

Enter the distance, your vehicle's efficiency and the fuel price.

How to use this tool

  1. Enter the journey distance and pick kilometres or miles.
  2. Enter your vehicle's fuel economy and select the unit it is quoted in — L/100 km, km per litre, US MPG or imperial MPG.
  3. Enter the fuel price and say whether it is per litre, per US gallon or per imperial gallon.
  4. Optionally split the cost between passengers.

Formula and method

Normalising the economy figure

km/L from L/100km:  100 ÷ value
km/L from US MPG:   value × 1.609344 ÷ 3.785411784
km/L from imp MPG:  value × 1.609344 ÷ 4.54609

Everything is converted to kilometres per litre first, so a single calculation handles all four input formats. The gallon figures are the exact international definitions.

Cost

litres = distance in km ÷ km per litre
cost = litres × price per litre

Worked examples

A 500 km trip at 8 L/100 km with fuel at 1.50 per litre

  1. Economy in km/L: 100 ÷ 8 = 12.5
  2. Fuel needed: 500 ÷ 12.5 = 40 litres
  3. Cost: 40 × 1.50 = 60

60 in fuel, or 0.12 per kilometre.

Why the two MPG figures differ

  1. 30 US MPG is 30 miles per 3.785 litres = 12.75 km/L
  2. 30 imperial MPG is 30 miles per 4.546 litres = 10.62 km/L

The same number means a less efficient car when quoted in imperial MPG.

Notes and limitations

  • The manufacturer's quoted economy is measured in laboratory conditions. Real-world consumption is usually 10–25% worse, and considerably worse in cold weather, heavy traffic or with a full load.
  • US and imperial gallons are different volumes. A car rated at 30 imperial MPG uses more fuel per litre than one rated at 30 US MPG, despite the identical number.
  • The calculation covers fuel only. Tolls, parking, wear and depreciation are excluded — for a full cost-per-mile figure those often exceed the fuel.
  • For an electric vehicle this tool does not apply; energy is priced per kWh rather than per volume.

Frequently asked questions

How do I calculate the fuel cost of a trip?

Divide the distance by your fuel economy to get the volume of fuel needed, then multiply by the price. The calculator handles the unit conversions so the two figures do not have to be in matching systems.

What is the difference between US and imperial MPG?

The gallon. A US gallon is 3.785 litres and an imperial gallon is 4.546 litres, about 20% larger. So 40 imperial MPG is roughly 33 US MPG for the same car.

How do I convert L/100km to MPG?

Divide 235.215 by the L/100km figure for US MPG, or 282.481 for imperial MPG. Alternatively just enter your figure above in whichever unit you have and let the calculator normalise it.

Why is my real fuel consumption worse than the official figure?

Official figures come from standardised test cycles that are gentler than real driving. Cold starts, short journeys, high speeds, air conditioning, roof boxes and heavy loads all increase consumption. Using your own observed economy gives a far better estimate.

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