MPG Converter (UK/US/L per 100km)

How MPG Converter (UK/US/L per 100km) works

Fuel-economy figures appear in three main units worldwide: miles per imperial gallon (used in several countries), US miles per US gallon, and liters per 100 kilometers (L/100km). This tool converts any of these three inputs into the other two, enabling direct comparison of manufacturer figures or trip-computer readings across regions. The calculation hinges on two official volume definitions and the mathematical relationship between distance-per-volume and volume-per-distance formats.

The formula

The converter uses fixed constants derived from the imperial and US gallon definitions:
Imperial MPG ↔ L/100km: L/100km = 282.481 ÷ Imperial MPG
US MPG ↔ L/100km: L/100km = 235.215 ÷ US MPG
Imperial MPG ↔ US MPG: US MPG = Imperial MPG × (3.78541 ÷ 4.54609)
The constants 282.481 and 235.215 are derived by converting one mile (1.60934 km) and the respective gallon volumes into the ratio form (100 × gallon_liters ÷ miles_per_km). The tool applies whichever pair of conversions matches the input unit, then displays all three results plus km/L (the reciprocal of L/100km × 100).

Where this method is most accurate

The conversions are mathematically exact when the input value itself is accurate. Real-world fuel-economy figures depend on driving style, terrain, tire pressure, vehicle load, and ambient temperature; this tool assumes the MPG or L/100km figure entered reflects true consumption under known conditions. The output precision is limited to one decimal place for MPG values and two for L/100km, which is sufficient for trip-computer and manufacturer-quoted data.

What this tool does not do

This calculator performs unit conversion only; it does not measure actual fuel consumption, estimate future economy, or account for differences in test cycles (WLTP, EPA, NEDC). It does not adjust for altitude, ethanol content, or differences between real-world and laboratory conditions. The tool assumes standard temperature and pressure for the gallon definitions and does not incorporate jurisdiction-specific correction factors.

Disclaimer

This tool is provided for educational and informational purposes. It performs mathematical unit conversion and does not constitute vehicle advice, emissions certification, or a guarantee of any specific fuel economy. Users remain responsible for verifying manufacturer specifications and complying with applicable regulations in their jurisdiction.