Fuel Economy Converter
By KAMP Inc. / UnitOwl · Last reviewed:
Fuel economy measures how efficiently a vehicle uses fuel — a number that affects both your wallet and the environment. The challenge is that different countries use fundamentally different ways to express this: miles per gallon (mpg) in the US and UK, liters per 100 kilometers (L/100km) in Europe, Australia, and most of the world, and sometimes kilometers per liter (km/L) in Asia. These aren't just different scales — they're inverse relationships, which makes intuitive comparison tricky.
Popular Fuel Economy Conversions
MPG vs. L/100km: An Inverse Relationship
MPG measures how far you travel on a fixed amount of fuel — higher is better. L/100km measures how much fuel you consume per fixed distance — lower is better. They are inversely related: L/100km = 235.215 / mpg (US). A 30 mpg car uses about 7.84 L/100km; a 50 mpg hybrid uses about 4.71 L/100km. This inverse relationship means that the fuel savings from improving from 10 to 20 mpg (5 L/100km improvement) are much larger than the savings from going 40 to 50 mpg (1.2 L/100km improvement), even though the mpg gains look similar. Beware: UK and US gallons differ — a UK gallon is 4.546 liters vs. 3.785 liters for a US gallon, so UK mpg figures are about 20% better than US mpg for the same vehicle.
| MPG (US) | L/100km |
|---|---|
| 10 mpg (US) | 23.5 L/100km |
| 20 mpg (US) | 11.76 L/100km |
| 30 mpg (US) | 7.84 L/100km |
| 40 mpg (US) | 5.88 L/100km |
| 50 mpg (US) | 4.70 L/100km |
| 60 mpg (US) | 3.92 L/100km |
Real-World Fuel Consumption and Cost
Fuel economy ratings from manufacturers are measured under controlled lab conditions and typically overstate real-world results by 15–25%. Aggressive driving, highway speeds above 70 mph, cold weather, air conditioning, and cargo all reduce fuel economy. For cost comparison: a 25 mpg vehicle driving 12,000 miles per year uses 480 gallons; at $3.50/gallon that is $1,680/year in fuel. A 35 mpg vehicle uses 343 gallons: $1,200/year — a savings of $480 annually. For the same vehicle in Europe at 8 L/100km and 15,000 km/year: 1,200 liters; at €1.60/liter that is €1,920/year. The difference in fuel price between the US and Europe (due to taxation) makes L/100km improvements more financially significant in Europe.
Electric Vehicles: MPGe and kWh/100 miles
Electric vehicles use different efficiency metrics. The EPA rates EVs in MPGe (miles per gallon equivalent) — calculated by equating 33.7 kWh of electricity to the energy content of one gallon of gasoline. A Tesla Model 3 rated at 130 MPGe means it travels as far on 33.7 kWh as a 130 mpg gasoline car travels on a gallon. More practically, EVs are often rated in kWh per 100 miles or Wh/mile: a vehicle using 3 miles/kWh (or 33 kWh/100 miles) at $0.15/kWh costs about $1.65 per 100 miles in electricity, compared to a 30 mpg gasoline car at $3.50/gallon costing $11.67 per 100 miles. In Europe, the equivalent metric is kWh/100km.
Sources & References
- NIST — Units and Conversion Factors — Official unit conversion factors from the National Institute of Standards and Technology.
- BIPM — The International System of Units (SI) — International SI unit definitions from the International Bureau of Weights and Measures.