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Convert Miles per Gallon to Kilometers per Liter - Fuel Economy Converter

This converter translates fuel economy given in miles per gallon (mpg) into kilometers per liter (km/L). It uses standard international unit definitions so results are reproducible and suitable for reporting, planning trips, or comparing vehicles across metric and imperial systems.

By default the tool assumes the common US gallon definition unless you explicitly select or note an Imperial (UK) gallon. The underlying conversion is based on the internationally accepted length and volume unit definitions, not vehicle onboard rounding.

Results are given with practical notes about measurement uncertainty, rounding, and common real-world differences between calculated and onboard computer figures.

Updated Nov 16, 2025

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Methodology

We perform a unit-to-unit conversion using the defined relationships: 1 mile = 1.609344 kilometres, 1 US gallon = 3.785411784 litres, and 1 Imperial (UK) gallon = 4.54609 litres. These constants originate from national measurement authorities and international standards.

The conversion calculates kilometres per litre by converting the distance portion (miles → kilometres) and dividing by the volume portion (gallons → litres). For reporting precision we recommend matching the number of significant digits to your measurement method (vehicle trip computer, pump receipts, or laboratory-grade flows).

For regulatory and label contexts, consult official guidance from national agencies on which gallon definition to use and on required rounding rules; our citations include links to government and standards resources.

Worked examples

Example: 30 mpg (US) → km/L. Calculation: 30 × (1.609344 / 3.785411784) ≈ 30 × 0.4251437075 = 12.754 km/L. Report as 12.75 km/L if rounding to two decimal places.

Example (Imperial): 30 mpg (Imperial) → km/L. Use litres per Imperial gallon: 30 × (1.609344 / 4.54609) ≈ 10.62 km/L.

Key takeaways

This converter uses established unit definitions to convert mpg to km/L reliably. Verify whether the mpg value uses a US or Imperial gallon before converting.

For precise reporting match the rounding and measurement practices to your data source and consult the cited government and standards resources for regulatory requirements.

Expert Q&A

Does this converter assume US or Imperial (UK) gallons?

By default the underlying conversion examples use the US gallon (3.785411784 L). If your mpg value is based on the Imperial gallon (4.54609 L) use the Imperial factor. Check your vehicle's country of origin or fuel-economy label to confirm which gallon definition applies.

Why does the onboard trip computer disagree with my manual conversion?

Onboard computers estimate fuel used via fuel-flow sensors and may apply smoothing, filtering, or rounding. Manual conversions use distance and fuel volume measurements (odometer + pump volume) and the exact unit constants; both can differ due to sensor error, calibration, tire size, and driving conditions.

How precise are the conversion constants?

The length and volume constants used here are exact by international convention to the precision published by national metrology institutes. Practical precision should match your input data quality—pump dispensers, odometer resolution, and sample size determine meaningful significant digits.

How should I round results for reporting or labels?

Follow the relevant regulatory guidance for labels in your jurisdiction. When not constrained, round to two decimal places for consumer-facing reports and consider one decimal place for quick comparisons. For engineering or laboratory work, keep full precision until final reporting.

Can I convert L/100 km to km/L or mpg here?

Yes. Convert L/100 km to km/L by taking 100 divided by the L/100 km value. To go from L/100 km to mpg, first convert to km/L then apply the km/L to mpg conversion or use a dedicated L/100 km ↔ mpg converter that applies the same unit constants.

What real-world factors affect measured mpg or km/L?

Temperature (fuel density), fuel composition, pump calibration, tire pressure and diameter, driving style, traffic, and altitude all affect measured fuel economy. For regulatory or lab-grade measurements follow the standardized test procedures published by authorities.

Sources & citations