MPG vs L/100km: Comparing Fuel Economy Across Countries

July 14, 2025 • 4 min read

Shopping for a car across borders? American reviews cite MPG (miles per gallon), while European and Australian specs use L/100km (litres per 100 kilometres). These measure the same thing — efficiency — but in opposite ways, making direct comparison tricky.

The Key Conversions

Why the Units Are "Backwards"

• ▶ MPG (higher = better): Measures distance per unit of fuel — "how far can I go?"
• ▶ L/100km (lower = better): Measures fuel per unit of distance — "how much fuel do I use?"
• ▶ This inverse relationship means the conversion is not a simple multiplication

Common Values Compared

• ▶ 15 MPG = 15.7 L/100km (large SUV/truck)
• ▶ 25 MPG = 9.4 L/100km (average car)
• ▶ 30 MPG = 7.8 L/100km (efficient sedan)
• ▶ 40 MPG = 5.9 L/100km (hybrid/efficient diesel)
• ▶ 50 MPG = 4.7 L/100km (excellent hybrid)
• ▶ 60 MPG = 3.9 L/100km (top hybrid efficiency)

US MPG vs UK MPG

Because the Imperial gallon is larger than the US gallon:

• ▶ A car getting 30 US MPG = 36 UK MPG (same car, same fuel use, different gallons)
• ▶ To convert: UK MPG = US MPG × 1.201
• ▶ UK car reviews always quote Imperial MPG — do not compare directly with US figures

Real-World vs Official Figures

• ▶ Official test figures (WLTP/EPA) are measured under controlled conditions
• ▶ Real-world consumption is typically 10-20% worse than official numbers
• ▶ Aggressive driving, short trips, cold weather, and air conditioning all reduce efficiency
• ▶ Highway driving at steady speed gives the best fuel economy

Quick Fuel Cost Comparison

To compare running costs between countries, you need both the fuel price and the consumption rate. A car doing 7 L/100km with fuel at $1.50/L costs $10.50 per 100 km. The same car in the US at $3.50/gallon costs about $9.40 per 100 km (62 miles).