Fuel economy converter
v1consumounidad_origenunidad_destinoconsumo_convertidoHow it is worked out
Convert fuel economy between miles per gallon (US or UK), kilometres per litre, kilometres per gallon and litres per 100 km, with exact factors.
Fuel economy is stated in two opposite ways: how far a quantity of fuel takes you (mpg, km/L, km per gallon) or how much fuel a distance uses (L/100 km). Going from one to the other means inverting the number, and between gallons, litres, miles and kilometres the factors are exact: a US gallon is 3.785411784 litres and a mile is 1.609344 kilometres.
The expression that runs
unidad_destino == "l_100km" ? 100 / (unidad_origen == "l_100km" ? 100 / consumo : consumo * buscar(km_por_litro, unidad_origen)) : (unidad_origen == "l_100km" ? 100 / consumo : consumo * buscar(km_por_litro, unidad_origen)) / buscar(km_por_litro, unidad_destino)The fields arrive with an example filled in: put your own numbers in and run it again. You can also edit the formula to fit your case.
What if the formula were yours?
This calculator is not hand-written: it is an Axioma formula. Open it in the editor to see how it is built, adapt it to your case and create the ones you need.
Why 40 km per gallon is 9.46 litres per 100 km
A US gallon holds 3.785411784 litres. If a car covers 40 kilometres on a gallon, it covers 40 divided by 3.785 on a litre, which is 10.57 kilometres. That is its fuel economy in kilometres per litre.
Litres per 100 kilometres measure the opposite: not how far you go, but how much you burn. They come from dividing 100 by the kilometres per litre, and 100 over 10.57 is 9.46 litres. That is why a higher number is better in km per gallon and worse in L/100 km.
US gallons and imperial gallons are not the same
The United States and Colombia sell fuel by the US gallon of 3.785 litres, while the United Kingdom uses the imperial gallon of 4.54609 litres, about 20 % larger. A car rated at 30 miles per gallon in the US shows up as 36 in a British brochure without using any less fuel.
When comparing specifications from different countries, it pays to bring everything to one unit. Litres per 100 kilometres are the reference across Europe and in most official test cycles, and they do not depend on which gallon is meant.
From fuel economy to the cost of a trip
With fuel economy in miles per gallon, a trip costs its distance divided by that economy, times the price of a gallon: 300 miles in a 30 mpg car is 10 gallons, which at 3.50 dollars a gallon comes to 35 dollars for the journey.
If what you have is litres per 100 kilometres, convert first or move the price to litres. This converter and the fuel cost calculator together answer what any journey costs, starting from the figures in any brochure.
Frequently asked questions
- How many km per litre is 30 mpg?
- It is 12.75 km/L: 30 miles are 48.28 kilometres, and a US gallon is 3.785 litres, so 48.28 divided by 3.785. In litres per 100 km the same car uses 7.84.
- What is good fuel economy in mpg?
- For a mid-size petrol car, anything above 35 mpg in the US measure is efficient, which is about 6.7 litres per 100 km. Below 25 mpg, over 9.4 L/100 km, consumption is on the high side for a passenger car.
- Why can L/100 km not be converted by multiplying?
- Because it measures the inverse: burning twice as much does not mean going twice as far. Going from L/100 km to km/L means dividing 100 by the number, so the conversion is not a simple proportion like pounds to kilograms or Celsius to Fahrenheit.