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

This converter converts fuel economy expressed as miles per imperial gallon (MPG UK) into liters consumed per 100 kilometers (L/100km). Enter a single MPG (UK) value to get the equivalent L/100km value used commonly in Europe and for regulatory comparison.

Results use internationally accepted unit definitions and published constants. The tool reports L/100km derived from exact definitions for the imperial gallon and the mile; see methodology and citations for authoritative sources and accuracy caveats.

Updated Nov 12, 2025

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Methodology

Calculation uses fixed unit definitions: 1 imperial gallon = 4.54609 liters and 1 mile = 1.609344 kilometers. These are stable international definitions used in measurement standards and referenced by national metrology institutions.

Numerical computation follows standard floating-point practice (IEEE 754 double precision) and is suitable for typical vehicle fuel-economy ranges. Rounding is applied only for display; underlying calculation uses full double-precision arithmetic. For traceability and unit correctness, consult NIST and ISO references listed in citations.

Worked examples

MPG(UK) = 40 → L/100km ≈ 282.480936 / 40 = 7.0620 L/100km

MPG(UK) = 30 → L/100km ≈ 282.480936 / 30 = 9.4160 L/100km

MPG(UK) = 60 → L/100km ≈ 282.480936 / 60 = 4.7080 L/100km

Key takeaways

This is a direct unit conversion using exact unit definitions; no empirical corrections are applied.

Use the numeric formula L/100km = 282.480936 / MPG(UK) for quick manual calculations or verification.

Expert Q&A

Is this conversion exact?

The conversion is exact given the defined constants for the imperial gallon (4.54609 L) and the mile (1.609344 km). The displayed result may be rounded for readability; the underlying arithmetic uses standard double-precision floating point. Small differences can arise from rounding and display formatting.

How does UK/Imperial MPG differ from US MPG?

UK (imperial) and US gallons are different volumes. One imperial gallon is 4.54609 liters while one US gallon is 3.785411784 liters. This converter specifically expects miles per imperial gallon (MPG UK). Using a US-MPG value will produce an incorrect L/100km result.

What input range is sensible?

Typical road vehicle values for MPG (UK) range roughly from 5 to 200. Values below 1 or extremely large values may indicate input error. The calculation itself accepts any positive numeric input but negative or zero values are invalid for fuel economy.

How accurate is the numeric output?

Accuracy is constrained by the defined conversion constants and floating-point representation (IEEE 754). For regulatory or legal purposes, use the exact constants cited and follow local measurement protocols. This tool is suitable for everyday comparisons, planning, and reporting but not a substitute for certified measurement when required.

Can I use this for emissions or cost estimates?

This converter provides only unit conversion between MPG (UK) and L/100km. Emissions or fuel cost calculations require additional inputs (fuel carbon intensity, fuel price, driving distance) and are outside the scope of this tool.

Sources & citations