MPG to L/100km — EU vs US Fuel Economy Explained
MPG (miles per gallon) and L/100km (liters per 100 kilometers) are inverse measurements. Higher MPG means better efficiency; lower L/100km means better efficiency. To convert: L/100km = 235.215 ÷ MPG (US gallon). To go back: MPG = 235.215 ÷ L/100km.
Why the Scales Go in Opposite Directions
MPG asks "how far can you go on one unit of fuel?" More distance per gallon = better. L/100km asks "how much fuel do you need to travel 100 km?" Less fuel per 100 km = better.
This inverse relationship means you cannot compare numbers directly. A car rated at 30 MPG (US) is equivalent to 7.84 L/100km — not 30 anything in metric. A car rated at 5 L/100km converts to 47.0 MPG (US) — more fuel efficient than the 30 MPG car, despite the smaller number.
The conversion formula uses 235.215 because that is the result of converting 100 km to miles (62.137) multiplied by liters per US gallon (3.78541). The constant is exact given the definitions of km, miles, liters, and US gallons.
Conversion Table
US MPG to L/100km and back — common fuel economy values.
- 15 MPG = 15.68 L/100km (large truck)
- 20 MPG = 11.76 L/100km (large SUV)
- 25 MPG = 9.41 L/100km (average sedan)
- 30 MPG = 7.84 L/100km (efficient compact)
- 35 MPG = 6.72 L/100km (hybrid)
- 40 MPG = 5.88 L/100km (efficient hybrid)
- 50 MPG = 4.70 L/100km (Toyota Prius)
- 4 L/100km = 58.8 MPG
- 6 L/100km = 39.2 MPG
- 8 L/100km = 29.4 MPG
- 10 L/100km = 23.5 MPG
- 12 L/100km = 19.6 MPG
US Gallon vs UK Gallon in MPG
MPG in the US uses the US gallon (3.785 liters). MPG in the UK uses the imperial gallon (4.546 liters). This makes UK MPG figures about 20% higher than US MPG for the same car.
A car rated at 50 UK MPG converts to approximately 41.6 US MPG — or 5.65 L/100km. The formula for UK MPG to L/100km uses 282.48 instead of 235.215.
When reading automotive press from the UK, always check whether MPG figures are US or imperial. Car review sites from the UK universally use imperial MPG. US car reviews use US MPG. European reviews typically publish only L/100km to avoid the confusion entirely.
Real-World vs Official Figures
Official fuel economy figures (EPA ratings in the US; WLTP in Europe) are measured on standardized test cycles, not real driving conditions. Real-world fuel economy typically runs 10–20% worse than official figures due to aggressive acceleration, highway speeds above the test cycle, climate control use, and cold weather.
Apps like Fuelly aggregate real-world fuel economy data submitted by owners. The gap between EPA city/highway ratings and actual owner-reported consumption is well-documented and consistent: expect to use 10–20% more fuel than the window sticker claims.
Conclusion
MPG and L/100km measure the same thing on inverse scales. Formula: L/100km = 235.215 ÷ MPG (US gallon). Better efficiency = higher MPG = lower L/100km. Always check whether an MPG figure uses US or UK (imperial) gallons before comparing — the 20% difference is enough to change the ranking of two cars.
Frequently Asked Questions
How do I convert MPG to L/100km?
Divide 235.215 by the MPG figure. Example: 30 MPG = 235.215 ÷ 30 = 7.84 L/100km.
What is 30 MPG in L/100km?
30 MPG (US) = 7.84 L/100km.
What is 7 L/100km in MPG?
235.215 ÷ 7 = 33.6 MPG (US gallon).
Is higher MPG or lower L/100km more fuel efficient?
Both mean better efficiency. Higher MPG = better. Lower L/100km = better. They are inverse scales of the same measurement.
Does UK MPG equal US MPG?
No. UK MPG uses the imperial gallon (4.546 L); US MPG uses the US gallon (3.785 L). UK MPG figures are about 20% higher for the same car. Always check which gallon is used.