Fuel Efficiency Converter
Convert between mpg (US), mpg (UK), L/100km, and km/L fuel economy units.
What Is the Fuel Efficiency Converter?
The Fuel Efficiency Converter converts between all major fuel economy units: miles per gallon (MPG), liters per 100 kilometers (L/100km), kilometers per liter (km/L), and miles per liter (mi/L). Useful for international car comparisons, road trip planning, and environmental impact assessment.
Formula
How to Use
Enter your fuel efficiency value in any unit (MPG, L/100km, km/L, or mi/L). The converter instantly displays all equivalent values, so you can compare a US car rating (MPG) to a European rating (L/100km) with one click.
Example Calculation
30 MPG (US gallon): = 235.215/30 = 7.84 L/100km. = 30 miles ÷ 3.785L = 7.93 km/L. A European car rated at 6 L/100km: = 235.215/6 = 39.2 MPG = 16.67 km/L.
Understanding Fuel Efficiency Converter
Fuel efficiency describes how far a vehicle travels per unit of fuel consumed. The metric varies by country: the US uses miles per gallon (MPG), while Europe and most of the world use liters per 100 kilometers (L/100km), which is an inverse measure. Converting between these is essential when comparing vehicles across markets, planning international road trips, or evaluating the environmental impact of vehicle choices.
The non-intuitive inverse relationship between MPG and L/100km creates a common misconception about efficiency gains. Improving from 10 to 20 MPG (halving consumption) saves far more fuel than improving from 40 to 50 MPG, even though the MPG improvement is the same (10 MPG). The L/100km measure makes this more intuitive: 23.5 to 11.8 (saving 11.7 L) vs 5.9 to 4.7 (saving 1.2 L).
Fuel efficiency is increasingly important for environmental and cost reasons. Fuel economy standards — EPA CAFE standards in the US, WLTP in Europe — regulate fleet-average efficiency. Electric vehicles are rated in MPGe (miles per gallon equivalent), where 33.7 kWh of electricity is treated as equivalent to one gallon of gasoline for comparison purposes.
Frequently Asked Questions
Why do US and European fuel economy units seem to give very different numbers?
MPG and L/100km are inverse measures (more MPG = more efficient; less L/100km = more efficient). A 30 MPG car getting 7.84 L/100km is the same car — the units just express efficiency differently.
What is the difference between US and UK gallons?
1 US gallon = 3.785 liters. 1 UK (imperial) gallon = 4.546 liters. A car rated at 40 MPG (UK) = only 33 MPG (US). Always specify which gallon is used.
What is the EPA rating methodology?
The US EPA tests vehicles on standardized city and highway drive cycles. The combined MPG is 55% highway and 45% city. Real-world fuel economy typically differs from EPA estimates by 5–30% depending on driving style.
How does fuel efficiency affect CO₂ emissions?
Burning 1 liter of gasoline produces approximately 2.31 kg of CO₂. A car getting 8 L/100km emits about 185 g CO₂/km; one getting 5 L/100km emits about 116 g CO₂/km.
Is this converter free?
Yes, completely free with no registration required.