Understanding Fuel Economy Metrics
Fuel economy is a critical metric for vehicle owners, impacting both your wallet and the environment. However, depending on where you are in the world, the way fuel efficiency is measured varies dramatically.
In the United States and the United Kingdom, fuel efficiency is typically measured by distance per volume: Miles Per Gallon (MPG). In contrast, most countries using the metric system measure volume per distance: Liters per 100 Kilometers (L/100km). This inverse relationship can make conversions tricky without a dedicated tool.
The Difference Between US and UK MPG
A common point of confusion is the difference between US MPG and UK (Imperial) MPG. Although they use the same name, the size of a gallon differs between the two systems.
US Gallon: Approximately 3.785 liters.
UK Gallon: Approximately 4.546 liters (about 20% larger than a US gallon).
Because a UK gallon holds more fuel, a car will appear to get a higher MPG rating in the UK compared to the US, even if the actual efficiency is identical. Our calculator accurately handles this discrepancy.
Common Fuel Conversions
Understanding how to read L/100km is essential for international travel. Unlike MPG, where a higher number means better fuel efficiency, a lower number in L/100km indicates a more efficient vehicle (as it uses fewer liters to travel the same 100 kilometers).
| Efficiency Level |
US MPG |
L/100km |
| Excellent (Hybrid/EV) |
~50 MPG |
~4.7 L/100km |
| Good (Modern Sedan) |
~30 MPG |
~7.8 L/100km |
| Fair (SUV/Truck) |
~20 MPG |
~11.8 L/100km |
