Mileage Calculator
Calculate your vehicle's fuel economy from distance traveled and fuel used.
About the Mileage Calculator
Tracking your actual fuel economy — rather than relying on the manufacturer's rated MPG — gives a true picture of how a vehicle performs in your real-world driving. This calculator divides distance by fuel used to find your effective mileage, with an L/100km equivalent for comparison.
How It Works
The calculator divides the distance you traveled by the amount of fuel consumed to get a distance-per-fuel-unit figure (like miles per gallon), and converts it to liters per 100 km so you can compare it with metric fuel-economy ratings.
Fuel Economy = Distance ÷ Fuel Used. L/100 km = 100 × liters ÷ kilometers, which equals 235.215 ÷ mpg when you enter miles and US gallons.
Worked example
Scenario: Driving 350 miles on 12.5 US gallons.
- Fuel economy: 350 ÷ 12.5 = 28 mpg.
- Convert to L/100 km: 235.215 ÷ 28 = 8.4 L/100 km.
- In km per liter: 28 × 1.609 ÷ 3.785 = 11.9 km/L.
Result: 28 mpg, equivalent to 8.4 L/100 km.
Tips and common mistakes
- Choose 'Kilometers & liters' for metric figures: 400 km on 30 L is 13.33 km/L, or 7.5 L/100 km.
- Fill the tank, reset the trip meter, drive, then refill and record the gallons — that gives the most accurate figure.
- UK (imperial) gallons are 20% larger than US gallons; convert them to liters first.
Assumptions & Limitations
- Assumes the distance and fuel amounts entered both correspond to the exact same trip or fill-up period, measured consistently.
- Choose miles and US gallons or kilometers and liters; the labels and the L/100 km conversion follow your choice.
- Real fuel economy varies trip to trip based on driving conditions — track several fill-ups over time for a more representative average.
Mileage can mean two different things
Fuel economy may be expressed as distance per unit of fuel (such as mpg or km/L) or fuel used per distance (such as L/100 km). These measures move in opposite directions: higher mpg is better, while lower L/100 km is better.
For a useful comparison, use the same units, fill-up method and driving conditions across trips. Short samples can be distorted by traffic or partial refuelling.