Engineering
Fuel Economy Converter Calculator
Fuel economy is reported in miles per gallon (MPG) in the US and UK, and in liters per 100 km (L/100km) in most other countries. However, the US gallon (3.785 L) and imperial gallon (4.546 L) are different — a UK MPG figure cannot be directly compared to a US MPG figure. This calculator converts between all three systems accurately.
Calculator
Formula
Formula
L/100km = 235.214 / MPG(US) MPG(US) = 235.214 / L/100km
The constants come from unit conversions: 1 mile = 1.60934 km; 1 US gallon = 3.78541 L. So 100 km / 1 mile × 3.78541 L = 235.214. For imperial MPG: 1 imperial gallon = 4.54609 L, so the constant is 282.481. MPG(imp) = MPG(US) × (4.54609 / 3.78541) = MPG(US) × 1.20095.
Worked example
A car achieves 35 MPG (US). Convert to L/100km and MPG (imperial).
- 1.L/100km = 235.214 / 35 = 6.72 L/100km
- 2.MPG (imperial) = 35 × 1.20095 = 42.03 mpg (imp)
35 MPG (US) = 6.72 L/100km = 42.0 MPG (imperial).
Assumptions and limitations
- Uses US liquid gallon = 3.785411784 L exactly.
- Uses imperial gallon = 4.54609 L exactly.
- Assumes steady-state fuel economy (no cold-start or driving-cycle correction).
- L/100km is a consumption metric (lower = better); MPG is an economy metric (higher = better).