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Convert Miles per Gallon to Miles per Gallon UK - Fuel Economy Converter

This converter translates fuel economy reported in miles per US gallon (mpg, US) into miles per Imperial (UK) gallon (mpg, UK). The two units differ because the US gallon and the Imperial gallon have different volumes; converting between them uses internationally accepted definitions for those gallon volumes.

Use this tool when comparing vehicle ratings across markets (for example, EPA/DOE figures in the United States vs UK/European figures that use Imperial gallons) or to convert a measured/recorded mpg value for reporting, comparison, or regulatory compliance checks.

Updated Nov 19, 2025

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Methodology

The conversion relies on official volumetric definitions: 1 US gallon = 3.785411784 liters and 1 Imperial (UK) gallon = 4.54609 liters. Because an Imperial gallon contains more liters than a US gallon, a vehicle’s miles per Imperial gallon will be larger by the ratio of the two gallon volumes.

Practically, the converter applies the fixed unit relationship between the two gallon definitions. Where available, regulatory test-cycle values (EPA, DOE, or UK test methods) should be used for official comparisons since test procedures and rounding rules can also affect published figures.

For traceability and best practice, the underlying gallon-to-liter values follow national standards and measurement authorities (see citations). When performing reporting or compliance tasks, round according to the target authority’s rules (for example, EPA rounding conventions for US labels or UK measurement guidance).

Worked examples

Example 1: 30.0 mpg (US) → 30.0 × 1.200949925 ≈ 36.03 mpg (UK).

Example 2: 45.5 mpg (US) → 45.5 × 1.200949925 ≈ 54.61 mpg (UK).

To convert reported mpg values for publication or compliance, apply the same factor then round according to the receiving authority’s rules.

Further resources

Expert Q&A

Why do US mpg and UK mpg values differ even for the same car?

They differ because the US gallon and the Imperial (UK) gallon are different sizes. The Imperial gallon is larger (4.54609 L vs 3.785411784 L), so a vehicle will show a higher miles-per-gallon number when expressed per Imperial gallon. Test procedures and rounding rules used by regulators also affect published figures.

What is the exact conversion factor?

Multiply US mpg by 4.54609 ÷ 3.785411784 ≈ 1.200949925 to get Imperial (UK) mpg. The inverse factor is approximately 0.832674.

Should I use this conversion for regulatory labeling or just for informal comparison?

This conversion is mathematically correct for unit translation. For official labels or regulatory compliance, use the values and rounding rules specified by the relevant authority (for example, EPA/DOE rules in the US or UK measurement guidance).

How many significant digits should I keep?

Keep enough significant digits to reflect your measurement accuracy. For casual comparisons 2 decimal places is typically sufficient (for example, 36.03 mpg (UK)). For reporting or regulatory purposes, follow the destination authority’s rounding rules.

How does this relate to liters per 100 kilometers (L/100 km)?

L/100 km is a metric measure of fuel consumption used in many countries. Convert mpg (US or UK) to L/100 km via liters and kilometers conversions; authoritative references such as DOE/EPA provide conversion guidance and calculators for mpg ↔ L/100 km.

Are reported manufacturer mpg figures directly comparable across countries?

Not always. Different countries can use different test cycles and measurement standards. Unit conversion addresses only the unit-size difference; test-procedure differences must be considered when comparing official manufacturer figures.

Sources & citations