How the MPG calculator works
Enter the miles you drove and the gallons of fuel you used to refill, and the tool returns your miles per gallon. Add a fuel price and it also shows your cost per mile, cost per 100 miles, and the metric L per 100km equivalent, so you can track real-world efficiency rather than relying on the sticker figure.
Measuring real fuel economy
The accurate way to measure MPG is the fill-to-fill method: fill the tank, reset your trip meter, drive normally, then refill and note the gallons added. Miles driven divided by gallons added is your true MPG for that tank. Doing this over several tanks smooths out variation from one fill-up to the next.
Why your MPG varies
Fuel economy drops with city stop-and-go driving, high speeds, cold weather, short trips, low tire pressure, roof racks, and heavy loads. Tracking MPG over time helps you spot a sudden drop that might signal a maintenance issue, such as a failing sensor, dragging brakes, or underinflated tires.
MPG and cost per mile
Cost per mile is fuel price divided by MPG, a handy figure for budgeting and for comparing vehicles. The L per 100km conversion lets you compare against vehicles rated in metric units. These are fuel figures only and do not include maintenance, insurance, or depreciation.
Frequently asked questions
How do I calculate MPG? Divide the miles driven by the gallons used to refill the tank.
What is good gas mileage? It depends on the vehicle, but many modern cars average 25 to 35 MPG combined.
How do I convert MPG to L/100km? Divide 235.2 by your US MPG; the tool shows this automatically.