How to use this calculator
Replace the example values with your own measurements or specifications. Keep the units shown beside each label. Results update as you type; reset restores the example.
A higher MPG or km/L value means more distance per unit of fuel. A lower L/100 km value means less fuel per distance. The calculation uses 1 mile = 1.609344 km, 1 U.S. liquid gallon = 231 cubic inches = 3.785411784 liters, and 1 Imperial gallon = 4.54609 liters. These conversions do not make different vehicle test cycles directly comparable.
The formula
A worked example
30 U.S. mpg equals 7.84 L/100 km, 36.03 UK mpg, and 12.75 km/L. Starting with 8 L/100 km instead gives 29.40 U.S. mpg, 35.31 UK mpg, and 12.50 km/L. Calculations retain full precision internally; displayed results are rounded.
Fuel economy conversion table
Equivalent fuel efficiencies, rounded to two decimal places. Use the calculator above for your exact input.
| U.S. mpg | UK / Imperial mpg | L/100 km | km/L |
|---|---|---|---|
| 10.00 | 12.01 | 23.52 | 4.25 |
| 15.00 | 18.01 | 15.68 | 6.38 |
| 20.00 | 24.02 | 11.76 | 8.50 |
| 25.00 | 30.02 | 9.41 | 10.63 |
| 30.00 | 36.03 | 7.84 | 12.75 |
| 35.00 | 42.03 | 6.72 | 14.88 |
| 40.00 | 48.04 | 5.88 | 17.01 |
| 45.00 | 54.04 | 5.23 | 19.13 |
| 50.00 | 60.05 | 4.70 | 21.26 |
| 60.00 | 72.06 | 3.92 | 25.51 |
Common questions
How do I convert L/100 km to MPG?
Select L/100 km as the input unit and enter your consumption. The calculator gives both U.S. and UK MPG. For example, 8 L/100 km is 29.40 U.S. MPG or 35.31 UK MPG.
Why is UK MPG higher than U.S. MPG?
An Imperial gallon contains more fuel than a U.S. liquid gallon. The same fuel efficiency therefore has a UK MPG figure about 20.1% higher. This is a unit difference, not an efficiency improvement.
Why does the conversion use division?
MPG measures distance per fuel volume. L/100 km measures fuel volume per distance, so the relationship is reciprocal. Halving L/100 km doubles MPG.
Can I average two MPG figures to estimate fuel use?
For a measured overall MPG, divide total miles by total gallons. An arithmetic average of MPG figures can misstate the result. For equal-distance trips, averaging L/100 km is appropriate.
Why is zero not accepted?
A finite conversion between these reciprocal measures requires a positive input. Zero fuel consumption would imply infinite distance per fuel unit, which this calculator cannot represent.
Sources & calculation method
Related guidance: NIST: conversion factors by quantity. Accessed September 9, 2026. The equation above describes this tool’s model; the reference provides practical context and does not endorse this site.
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