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Fuel Efficiency Calculator

Convert fuel efficiency instantly across US MPG, Imperial (UK) MPG, Liters per 100 Kilometers (L/100 km), and Kilometers per Liter (km/L).

Calculation Results

Fuel Efficiency Conversion Formulas

L/100km = 235.215 / US MPG | UK MPG = US MPG × 1.20095 | km/L = US MPG × 0.425144
  • US vs. UK Gallon: A UK Imperial gallon equals 4.546 liters, while a US gallon equals 3.785 liters. UK MPG numbers are always ~20% higher for the exact same vehicle.
  • Inverse Scale: Lower L/100km represents superior fuel efficiency, whereas higher MPG represents superior efficiency.

Step-by-Step Worked Example

Scenario: Converting 30.0 US MPG to international standards

Calculation Steps:

  1. UK (Imperial) MPG = 30.0 × 1.20095 = 36.03 UK MPG
  2. Liters per 100 km = 235.215 / 30.0 = 7.84 L/100km
  3. Kilometers per Liter = 30.0 × 0.425144 = 12.75 km/L
  4. Gallons needed for 100 miles = 100 / 30 = 3.33 gallons
Result: 30.0 US MPG equals 36.0 UK MPG, 7.84 L/100 km, or 12.75 km/L.

How to Use This Calculator

  1. 1Enter the efficiency number from your dashboard or vehicle specs.
  2. 2Select your source unit (US MPG, UK MPG, L/100km, or km/L).
  3. 3Instantly see all equivalent international ratings.

Assumptions & Limitations

  • Uses standard NIST and ISO automotive conversion constants.

Frequently Asked Questions

Why are British car reviews reporting much higher MPG numbers?

The UK Imperial gallon is 20% larger than the US liquid gallon (4.546 L vs 3.785 L). A European car achieving 48 UK MPG is actually getting 40 US MPG.

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