Fuel Efficiency Calculator – MPG and L/100km from Distance and Fuel Used
Free fuel efficiency calculator: enter distance traveled and fuel used to get mpg or L/100km. Track real-world fuel economy across tanks. No sign-up, runs in your browser.
Fuel Efficiency Calculator
Enter distance traveled and fuel used to calculate mpg or L/100 km.
How the fuel efficiency calculator works
Efficiency = distance ÷ fuel used. The calculator converts units as needed:
mpg = miles ÷ gallons
L/100km = (liters ÷ km) × 100
For example, 400 km on 32 liters gives 8 L/100km. The same trip in miles and gallons would yield the equivalent mpg. Use this to track efficiency over multiple fill-ups.
Understanding fuel efficiency and how to improve it
Fuel efficiency tells you how far your vehicle travels on a unit of fuel. In the US, it's usually expressed as miles per gallon (mpg): higher is better. In most other countries, it's liters per 100 kilometers (L/100km): lower is better. The two are inversely related—a car that gets 30 mpg uses about 7.8 L/100km.
To get an accurate real-world figure, fill your tank, reset the trip odometer or note the mileage, drive until you need fuel again, then fill up and note how much you added. Enter the distance and fuel used into this calculator. Repeat over several tanks and average the results to smooth out variations from traffic, weather, and driving style.
Many factors affect efficiency: speed (most cars are most efficient around 50–60 mph), tire pressure, load, and maintenance. Aggressive acceleration and braking waste fuel. Use cruise control on the highway when safe. Keeping tires properly inflated and the engine tuned can improve efficiency by several percent.
When shopping for a new vehicle, compare EPA ratings, but remember that real-world numbers often differ. This calculator helps you establish your own baseline. Pair it with the fuel cost calculator to see how much you spend on fuel for your typical driving and to compare the cost of different vehicles over time.