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Fuel Consumption Calculator

AutomotiveFuel Economy and Running Costs
Measured in
Fuel consumption (L/100 km) —
Kilometres per litre
—
Miles per US gallon
—
Miles per UK gallon
—

Fuel consumption is the fuel used divided by the distance, times 100, giving litres per 100 km. If you drove 500 km and refilled 35 litres, consumption is 35 ÷ 500 × 100 = 7.0 L/100 km, which equals 14.29 km/L, 33.6 US mpg or 40.35 UK mpg.

About this tool

Drivers comparing a new car against its brochure figure, fleet managers checking a van after a service, and anyone moving between countries all run into the same problem: fuel economy is quoted in incompatible units. Europe uses litres per 100 km, much of Asia uses km per litre, and the US and UK both say mpg but mean gallons of different sizes. Enter the distance from your trip meter and the fuel you put back in at the pump, in kilometres and litres or in miles and US gallons, and the calculator returns all four figures at once with the working. The result is only as good as the measurement: a fill-to-full on the same pump over a full tank is far steadier than a single short trip or a dashboard estimate.

How to use it

  1. Pick your units

    Choose kilometres and litres, or miles and US gallons, to match your odometer and fuel receipt.

  2. Enter the distance

    Use the trip meter reading since the last full fill-up.

  3. Enter the fuel used

    Use the amount pumped to refill the tank to full, from the receipt.

  4. Read the four figures

    L/100 km is the headline; km/L, US mpg and UK mpg sit beside it, with the conversion steps below.

Examples

300 miles on 10 US gallons

Measured in
Miles and US gallons
Distance driven
300
Fuel used
10

Result Fuel consumption (L/100 km): 7.84
Kilometres per litre: 12.75
Miles per US gallon: 30
Miles per UK gallon: 36.03

  1. 300 mi × 1.609344 = 482.8 km; 10 US gal × 3.785411784 = 37.854 L
  2. L/100 km = 37.854 ÷ 482.8 × 100 = 7.84
  3. km/L = 482.8 ÷ 37.854 = 12.75
  4. US mpg = 235.215 ÷ 7.84 = 30; UK mpg = 282.481 ÷ 7.84 = 36.03

30 US mpg works out to 7.84 L/100 km, and the larger imperial gallon lifts the UK figure to about 36 mpg.

500 km on 35 litres

Measured in
Kilometres and litres
Distance driven
500
Fuel used
35

Result Fuel consumption (L/100 km): 7
Kilometres per litre: 14.29
Miles per US gallon: 33.6
Miles per UK gallon: 40.35

  1. L/100 km = 35 ÷ 500 × 100 = 7
  2. km/L = 500 ÷ 35 = 14.29
  3. US mpg = 235.215 ÷ 7 = 33.6; UK mpg = 282.481 ÷ 7 = 40.35

35 L over 500 km is 7 L/100 km, a typical figure for a mid-size petrol car on mixed roads.

20 km on 2 litres

Measured in
Kilometres and litres
Distance driven
20
Fuel used
2

Result Fuel consumption (L/100 km): 10
Kilometres per litre: 10
Miles per US gallon: 23.52
Miles per UK gallon: 28.25

  1. L/100 km = 2 ÷ 20 × 100 = 10
  2. km/L = 20 ÷ 2 = 10
  3. US mpg = 235.215 ÷ 10 = 23.52; UK mpg = 282.481 ÷ 10 = 28.25

A short city run at 10 L/100 km; the tool flags that a trip this short gives a rough reading.

How it is calculated

L/100 km = fuel (L) ÷ distance (km) × 100; US mpg = 235.215 ÷ (L/100 km); UK mpg = 282.481 ÷ (L/100 km)

fuel
Fuel used to cover the distance, in litres (US gallons × 3.785411784)
distance
Distance driven, in kilometres (miles × 1.609344)
235.215
100 × 3.785411784 ÷ 1.609344, the L/100 km to US mpg constant
282.481
100 × 4.54609 ÷ 1.609344, the L/100 km to UK mpg constant

Miles and US gallons are first converted with their exact legal definitions, so both unit choices run through the same metric formula. L/100 km is a consumption measure (lower is better), while km/L and mpg are economy measures (higher is better); they are reciprocals, which is why the mpg constants are divided by consumption rather than multiplied.

When not to use it

  • Not for electric cars, which are measured in kWh per 100 km.
  • Not for predicting a trip's fuel bill without a price; this gives consumption only.
  • Not reliable from a partial fill, since the fuel used is unknown.

Common mistakes

  • Mixing US and UK gallons, which differ by about 20 percent.
  • Using the dashboard range estimate instead of the pumped volume.
  • Measuring over one short trip, where a cold start skews the figure.
  • Comparing L/100 km and mpg as if higher were better in both.

Frequently asked questions

How do I measure the fuel used accurately?

Fill the tank until the pump clicks off, reset the trip meter, drive normally, then fill again at the same pump. The litres or gallons on the second receipt are the fuel used for the distance on the trip meter.

Why is UK mpg higher than US mpg for the same car?

A UK imperial gallon is 4.54609 litres, while a US gallon is 3.785411784 litres. The imperial gallon is about 20 percent larger, so a car covers more miles per imperial gallon: 30 US mpg equals about 36 UK mpg.

Is a lower L/100 km figure better?

Yes. L/100 km measures how much fuel is burned over a fixed distance, so a smaller number means a thriftier car. km/L and mpg run the other way, where a larger number is better.

Why does my result differ from the official rating?

Laboratory test cycles such as WLTP or the EPA cycle use set speeds, temperatures and loads. Real driving with air conditioning, roof racks, motorway speeds, cold starts and traffic usually burns 10 to 25 percent more than the label.

Where does the 235.215 constant come from?

One US gallon per mile equals 3.785411784 litres per 1.609344 km. Multiplying by 100 to get L/100 km gives 235.215, so dividing 235.215 by either L/100 km or US mpg returns the other.

Can I use this for a motorbike or a truck?

Yes. The calculation only needs distance and fuel, so it works for any vehicle burning liquid fuel, including diesel trucks, motorcycles, boats measured by distance, and generators on a vehicle.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 21). Fuel Consumption Calculator. Tools Directory. Retrieved October 27, 2026, from https://tools.milunir.com/automotive/fuel-economy-and-running-costs/fuel-consumption-calculator/

MLA

Tools Directory Editorial Team. “Fuel Consumption Calculator.” Tools Directory, 21 Oct. 2026, https://tools.milunir.com/automotive/fuel-economy-and-running-costs/fuel-consumption-calculator/. Accessed 27 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Fuel Consumption Calculator.” Tools Directory. Last modified October 21, 2026. Accessed October 27, 2026. https://tools.milunir.com/automotive/fuel-economy-and-running-costs/fuel-consumption-calculator/.

Link<a href="https://tools.milunir.com/automotive/fuel-economy-and-running-costs/fuel-consumption-calculator/">Fuel Consumption Calculator – Tools Directory</a>