Fuel Economy Converter

Background.

Fuel economy is reported in several units that do not all move in the same direction. Miles per gallon and kilometers per liter express distance divided by fuel, so higher values indicate more distance from a unit of fuel. Liters per 100 kilometers expresses fuel divided by distance, so lower values indicate less fuel use. This converter handles the reciprocal relationship as well as the different U.S. and Imperial gallon sizes.

Select the unit attached to the value you already have. “MPG” alone is ambiguous: one U.S. liquid gallon is exactly 3.785411784 liters, while one Imperial gallon is 4.54609 liters. Both results here use the international statute mile, exactly 1.609344 kilometers. A vehicle rated at 30 U.S. MPG therefore equals about 36.0285 Imperial MPG, 12.7543 km/L, or 7.84049 L/100 km.

The calculation converts every input through kilometers per liter. U.S. MPG is multiplied by 1.609344 km/mile and divided by 3.785411784 L/U.S. gallon. Imperial MPG uses 4.54609 L/Imperial gallon instead. Liters per 100 km is inverted as 100 divided by the entered value. The outputs are then derived from the same unrounded internal quantity, with rounding applied only to the displayed results.

Do not convert U.S. MPG to Imperial MPG by relabeling the number. Because the Imperial gallon is larger, the same physical fuel consumption has a numerically higher Imperial MPG. Conversely, L/100 km is not a linear “efficiency score”: doubling MPG halves fuel used per fixed distance, and halving MPG doubles it. EPA highlights this inverse relationship when explaining why consumption units can make fuel savings easier to compare.

A unit conversion preserves the underlying measurement; it does not change how that measurement was produced. Official label economy, a dashboard estimate, a laboratory cycle and a tank-to-tank calculation may describe different conditions. Before comparing vehicles or trips, confirm that values cover compatible city/highway cycles, fuels, distances, measurement methods and rounding conventions. Do not treat a converted laboratory rating as a promise of road performance.

For a tank-to-tank result, divide distance traveled by the fuel added only when the refill returns the tank to a comparable level. One fill can be distorted by pump cutoff, vehicle angle and small distance. Longer records are usually more representative. Weather, traffic, speed, elevation, tire pressure, payload, idling and driving style all affect real consumption, but none belongs in a pure unit conversion. Preserve the original unit beside every recorded value to prevent ambiguity later.

This page converts liquid-fuel volume economy only. It does not convert miles per gallon gasoline-equivalent, electric kWh/100 miles, mass-based fuel use or energy content. MPGe is an energy-equivalence metric, not a physical gallon of fuel, so passing it through a liquid-gallon converter would change its meaning. Use the units and methodology supplied by the original rating authority.

The dedicated conversion survives the catalog-neighbor check because the general Unit Converter does not contain a fuel-economy category. The MPG calculator handles distance and fuel quantities for a trip, while this page translates an already calculated rating. Use Fuel Cost after conversion when you also need price and travel distance.

What is fuel economy converter?

Fuel economy relates travel distance to fuel volume. US MPG, Imperial MPG and km/L are economy measures; L/100 km is their reciprocal consumption form.

How to use this calculator.

1. 01Identify whether an MPG value uses a U.S. or Imperial gallon.
2. 02Enter a positive value and select its exact unit.
3. 03Read all four equivalent units from the same unrounded conversion.
4. 04Compare only measurements produced under compatible conditions.

The formula.

All modes normalize to kilometers per liter. Reciprocal consumption is calculated by dividing 100 by km/L; U.S. and Imperial MPG use their legally distinct gallon volumes.

A worked example.

Frequently asked questions.

References& sources.

1. [1]NIST SP 811 Appendix B.9: gives the mile-to-kilometer factor and U.S. MPG-to-km/L and L/100 km relationships.
2. [2]NIST Handbook 130 (2026), §2.6.1: gives 3.785411784 liters per U.S. gallon.
3. [3]UK Weights and Measures Act 1985, Schedule 1 Part IV: defines the Imperial gallon as 4.54609 cubic decimeters.
4. [4]U.S. EPA, Text Version of the Gasoline Label: explains MPG, consumption units and their inverse comparison behavior.
5. [5]Natural Resources Canada, 2013 Fuel Consumption Guide, Conversions: independently publishes MPG and L/100 km relationships and distinguishes gallon sizes.