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Fuel Economy Converter

Convert fuel economy between miles per US gallon, miles per UK (imperial) gallon, kilometers per liter, miles per liter, liters per 100 km and US gallons per 100 miles. Units that measure distance per fuel and units that measure fuel per distance are reciprocals of each other, so the page uses division for those pairs and shows the formula it used. 30 mpg (US) is 7.84 L/100 km.

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Convert Fuel Economy

Fuel economy comes in two opposite forms: distance per fuel (mpg, km/L, higher is better) and fuel per distance (L/100 km, lower is better). The conversion between them is a reciprocal, not a multiplication.

Decimals and scientific notation such as 1.5e3 are accepted.
Automatic shows exact results in full and rounds long ones to 12 significant digits. A value too small for the chosen decimal places is shown with 3 significant digits instead of 0.

How to Use the Fuel Economy

  1. Type the value you want to convert in Value to convert.
  2. Pick the starting fuel economy unit in From unit and the one you want in To unit. The lists are grouped by measurement system.
  3. Read the result and the formula directly under the form; it updates as you type. Use Swap units to reverse the direction. Zero is explained rather than treated as an error.
  4. Scroll to the table to see the same value in every available unit, change Precision if you need fewer digits, or press Copy result.

About This Tool

Drivers comparing cars from the US, UK and Europe, buyers reading a used-car listing from another country, fleet managers and anyone converting an electric or fuel consumption figure for a budget.

Input: A number and a unit  ·  Output: The same fuel economy in every unit.

Features and Limitations

Features

  • Six units in two groups: distance per volume (mpg US, mpg UK, km/L, mi/L) and volume per distance (L/100 km, gal/100 mi).
  • Uses the exact US gallon (3.785411784 L), UK gallon (4.54609 L) and mile (1.609344 km).
  • Shows the reciprocal formula, for example L/100 km = 235.2146 ÷ mpg (US).
  • Handles zero by explaining that the matching value is undefined (infinite).

Limitations

  • The two mpg figures are not interchangeable: a UK gallon is 1.2009 times a US gallon, so the same car has a higher mpg in UK units.
  • Negative values are rejected because fuel economy cannot be negative. Average consumption over several trips should be calculated from total fuel and total distance, not by averaging mpg figures.
  • Results are computed in your browser; nothing you enter is sent to a server.

Example

30 mpg (US) = 7.84049 L/100 km = 12.754 km/L = 36.03 mpg (UK). 30 mpg (UK) = 9.416 L/100 km. 8 L/100 km = 29.40 mpg (US) = 35.31 mpg (UK). 15 km/L = 6.667 L/100 km. 40 mpg (US) = 2.5 gal/100 mi.

Frequently Asked Questions

How do I convert mpg to L/100 km?

Divide 235.2146 by the US mpg (or 282.4809 by the UK mpg). 30 mpg (US) gives 235.2146 ÷ 30 = 7.84 L/100 km. The same formula works in reverse, so 8 L/100 km is 235.2146 ÷ 8 = 29.4 mpg (US).

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

Because the UK (imperial) gallon is larger, 4.54609 L versus 3.785411784 L, the same distance on one gallon is a bigger number of miles. Multiply US mpg by 1.2009 to get UK mpg: 30 mpg (US) is 36.03 mpg (UK).

What happens when I enter zero?

0 mpg (or km/L) means no distance on any amount of fuel, so L/100 km is infinite and shows as undefined. 0 L/100 km means no fuel is used, so mpg is undefined. The converter explains this instead of showing an error.

Is a lower or higher number better?

For mpg and km/L, higher is better. For L/100 km and gal/100 mi, lower is better. That is why the page groups the units this way. Gallons per 100 miles is sometimes preferred because savings add up: going from 20 to 25 mpg saves 1 gal/100 mi, the same as from 50 to 100 mpg.

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