Fuel Cost Calculator
Calculate trip fuel cost from distance, efficiency and the price per unit.
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Fuel Economy Converter
MPG, litres per 100 km and km per litre, both gallons.
Fuel Economy Converter tool
Optional. Works out the fuel and the cost.
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Litres per 100 km
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Miles per US gallon
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Miles per imperial gallon
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Kilometres per litre
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Cost of the journey
| Measure | Value |
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Miles per gallon and litres per 100 km run in opposite directions: a higher mpg is better and a higher L/100km is worse. They are reciprocals, which is why improving from 20 to 25 mpg saves far more fuel than improving from 40 to 45.
About the Fuel Economy Converter
Fuel Economy Converter moves between the three ways fuel consumption is expressed and both kinds of gallon. Litres per 100 km in most of Europe, miles per gallon in Britain and America, kilometres per litre in much of Asia and South America.
Two traps make this worth a dedicated tool. The first is the gallon: an imperial gallon is 4.546 litres and a US gallon 3.785, so the same car is about twenty per cent more economical on paper in Britain than in America. A 35 mpg American car is 42 mpg imperial, and neither figure is wrong.
The second is that mpg and L/100km are reciprocals, not scales, which makes mpg a misleading measure of savings. Going from 20 to 25 mpg saves one gallon per hundred miles; going from 40 to 45 saves only a quarter of that, despite being the same five-mpg improvement. Litres per 100 km is linear in fuel used, which is why Europe standardised on it.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
Looking for something this does not cover? FreeToolsZone.org is more free browser-based tools, organised by job, and it is worth a look if fuel economy converter is only part of what you are working on.
How to use the Fuel Economy Converter
- Choose fromThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
- Enter value, journey distance (km) and fuel price per litreDecimals are fine, and thousands separators are accepted and ignored.
- Read the litres per 100 km, miles per us gallon and miles per imperial gallonThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row.
Features
- Shows litres per 100 km, miles per us gallon, miles per imperial gallon, kilometres per litre and cost of the journey together, so you are not running it twice
- A results table you can read across
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The fuel economy converter is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Converting a car specification between mpg and L/100km
- Comparing a US mpg figure with a British one
- Working out the fuel cost of a journey
- Comparing two cars on fuel used rather than distance covered
Frequently asked questions
Why is imperial mpg higher than US mpg?
Because an imperial gallon is 4.546 litres against the US 3.785. The same car covers more miles on the larger gallon, so the figure is about twenty per cent higher.
Which measure is better for comparing cars?
Litres per 100 km, because it is proportional to fuel used. mpg exaggerates the benefit of improvements at the efficient end of the range.
How do I convert mpg to L/100km?
Divide 235.21 by the US mpg figure, or 282.48 by the imperial one. The calculator does it exactly rather than with those rounded constants.
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Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.