MPG to L/100km Converter

How to use the mpg to l/100km converter

1. Enter your fuel economy value in miles per gallon.
2. Select whether the figure uses US gallons or UK (imperial) gallons.
3. Read the converted result in liters per 100 kilometers immediately.

How the mpg to l/100km formula works

The two units measure fuel economy in opposite directions. MPG tells you how far you travel on one gallon of fuel, while L/100km tells you how much fuel you burn over a fixed distance. Because they are inversely related, the conversion divides a constant by your MPG value.

The constant depends on which gallon you use. One mile equals exactly 1.609344 kilometers, so 100 km is 62.137119 miles. A US gallon is exactly 3.785411784 liters, and a UK gallon is exactly 4.54609 liters.

For US gallons the formula is:

L/100km = 235.214583 / MPG

For UK gallons the formula is:

L/100km = 282.481053 / MPG

Worked example: a car rated at 30 MPG (US) consumes 235.214583 divided by 30, which equals 7.84 L/100km. If that same number were measured in UK gallons, it would be 282.481053 divided by 30, or 9.42 L/100km.

Common fuel economy conversions

This table shows frequently referenced values when converting mpg to l/100km for both US and UK gallons. Use it as a quick reference alongside the calculator above.

Why the gallon type matters

A common mistake when converting fuel economy is ignoring the difference between US and UK gallons. The US liquid gallon is defined as exactly 231 cubic inches, which works out to 3.785411784 liters. The UK imperial gallon is larger: exactly 4.54609 liters. That is roughly a 20 percent difference in volume.

If you take a British fuel economy figure of 40 MPG and apply the US constant (235.21), you get 5.88 L/100km. But applying the correct UK constant (282.48) gives 7.06 L/100km. Using the wrong gallon type leads to significant errors, especially when comparing vehicles across markets or calculating trip costs with a tool like the fuel cost calculator.

Understanding inverse fuel economy scales

In the United States and the United Kingdom, higher numbers mean better efficiency because the unit measures distance per volume. In most other countries, including Canada, Australia and all of Europe, lower numbers are better because the unit measures volume per distance.

This inverse relationship means that improvements at low MPG values save more fuel than identical improvements at high MPG values. Going from 10 to 15 MPG saves about 7.84 liters per 100 km (US), while going from 40 to 45 MPG saves only about 0.65 liters per 100 km. The L/100km scale makes these differences linear and easier to compare directly.

Practical uses for this converter

Importing a vehicle from another country is the most common reason people need an mpg to l/100km conversion. A car listed at 35 MPG in an American auction needs to be understood in metric terms before you can compare its running costs to local vehicles.

Rental cars abroad also cause confusion. If you are used to reading fuel economy in miles per gallon but the rental dashboard or brochure lists consumption in liters per 100 kilometers, this converter helps you quickly gauge whether the vehicle is efficient. Similarly, automotive journalists and engineers frequently translate specifications between regional standards when reviewing international models.

Worked examples

Each result below was produced by the same code the tool runs, so you can check your own numbers against them.