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Fuel Economy Calculator

What is my fuel economy?

Result

7.00
14.29
33.60

How it is calculated

From the distance driven and the fuel burned, the tool gives three standard measures. Consumption in litres per 100 km: L/100km = fuel ÷ distance × 100. Efficiency in kilometres per litre: km/L = distance ÷ fuel. US miles per gallon: mpg = km/L × 2.35214583. Distance must be in kilometres and fuel in litres, and both must be greater than zero. Lower L/100 km is better, while higher km/L and mpg are better. The mpg figure is the US gallon; the imperial gallon is about 20% larger, so UK figures look higher. Results are rounded to two decimals.

Worked example

You drive 450 km and refill 31.5 litres to top up the tank. Consumption: 31.5 ÷ 450 × 100 = 7.00 L/100 km. Efficiency: 450 ÷ 31.5 = 14.29 km/L. In US miles per gallon: 14.29 × 2.35214583 = 33.60 mpg. The numbers are three views of one result: a car that burns 7 litres per 100 km covers about 14.3 km on each litre.

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Common mistakes

  • Entering miles and gallons. The fields expect kilometres and litres.
  • Comparing L/100 km with mpg as if both rose together: a higher mpg means better economy, a higher L/100 km means worse.
  • Calculating from a partial fill-up rather than a full tank to full tank, which makes the figure inaccurate.
  • Comparing a US mpg figure with a UK one. The two gallons are different sizes.

About this calculator

This tool calculates how efficiently a vehicle uses fuel by dividing the distance traveled by the amount of fuel consumed, presenting the result in the three most common formats — liters per 100 kilometers, kilometers per liter, and miles per gallon — since different countries and car specifications use different units. Entering a fill-up's distance and fuel amount converts a real trip into a number that is directly comparable against a manufacturer's rated fuel economy or a previous tank.

Drivers use it to track their actual fuel economy over time, which often differs from the official figures quoted by manufacturers due to driving style, terrain and traffic conditions, and to notice early warning signs of mechanical problems if consumption suddenly worsens. It is also useful when comparing two vehicles that list fuel efficiency in different units, or when budgeting fuel costs for a road trip based on a car's real-world consumption rather than its brochure rating.

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Comments (1)

  • Editorial team

    One tank is a noisy sample, so total up several fill-ups instead. Add all the kilometres and all the litres across, say, four or five tanks, then enter the two sums; this is more reliable than averaging the individual L/100 km figures. Keep the method steady too, always filling to the pump's first click at the same station. Winter, short city trips and roof boxes will all push the number up. How does your figure compare with the manufacturer's rating?

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