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Convert Liters per 100 Kilometers to Miles per Gallon - Fuel Economy Converter

This converter transforms fuel consumption expressed in liters per 100 kilometres (L/100 km) into miles per gallon (US). It is intended for drivers, fleet managers, and engineers who need a precise, standards-based conversion between metric and customary fuel-economy units.

The conversion relies on internationally recognised unit definitions (SI) and the US liquid gallon definition. For guidance on testing procedures and official labelling, consult national guidance from agencies such as the U.S. Department of Energy and the Environmental Protection Agency.

Updated Nov 16, 2025

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Methodology

We convert distance and volume using fixed unit relationships: 100 kilometres = 62.137119 miles (based on 1 mile = 1.609344 km) and 1 US liquid gallon = 3.785411784 litres. Combining those constants yields a single conversion constant.

For US miles per gallon the direct relationship is: MPG (US) = 235.214583 ÷ (L/100 km). The constant 235.214583 is derived from (100 km × miles-per-km) × litres-per-gallon and is consistent with NIST and DOE unit definitions.

Be aware there are two common MPG conventions: US (liquid gallon) and Imperial (UK) gallon. Use the appropriate conversion for the gallon definition required by your context or regulation.

Worked examples

Example 1: 5.0 L/100 km → 235.214583 ÷ 5.0 = 47.04 mpg (US).

Example 2: 6.5 L/100 km → 235.214583 ÷ 6.5 = 36.19 mpg (US).

Note: For Imperial gallons, use the Imperial constant ≈ 282.480936 (Imperial mpg = 282.480936 ÷ L/100 km).

Further resources

Expert Q&A

Which gallon does this converter use?

This converter uses the US liquid gallon (1 US gal = 3.785411784 L). If you need Imperial (UK) mpg, use the Imperial constant (different gallon definition) or switch to a converter configured for Imperial mpg.

Why is there a single constant (235.214583)?

The constant comes from combining exact unit relationships (100 km → miles and litres → US gallons). Using the constant is mathematically equivalent to performing the two unit conversions separately and is the standard approach used by regulatory bodies and technical references.

How many decimals should I report?

Display precision depends on context: consumer-facing displays commonly show one or two decimals; engineering or regulatory reports may use three or more. Rounding should reflect instrument accuracy and measurement uncertainty.

Will this match my car’s trip computer?

Trip computers use the vehicle’s fuel-flow sensor and distance measurement; they may apply smoothing algorithms and display rounded values. Small differences can arise due to sensor calibration, driving cycles, and rounding. For regulatory comparisons, use official test-cycle values published by agencies.

Are environmental conditions or test cycles relevant?

Yes. Official fuel economy figures are produced under standardized laboratory or on-road test cycles defined by regulatory agencies. Real-world fuel use varies with temperature, load, tyre pressure, driving style, and other factors.

How accurate is the conversion?

The mathematical conversion using the defined constants is exact to the precision of the constants. Real-world accuracy depends on how the L/100 km value was measured and the precision of instruments; consider measurement uncertainty when reporting results.

Sources & citations