MPG Calculator
Enter the miles you drove and the gallons you used to find your miles per gallon. The result also shows liters per 100 kilometers and the fuel cost per mile.
How to use this mpg calculator
- Fill the tank and reset the trip meter, or write down the odometer reading.
- Drive as you normally would, then fill the tank again at the same pump to the same level.
- Enter the miles driven and the gallons you added.
- Add the price per gallon if you want the cost per mile.
- Press Calculate. Repeat over a few tanks and average the results.
How to calculate miles per gallon
Fuel economy is the distance divided by the fuel used.
- Miles per gallon = miles driven / gallons used
- Liters per 100 km = liters used / kilometers driven x 100, where 1 mile = 1.609344 km and 1 US gallon = 3.785412 liters
- Kilometers per liter = kilometers driven / liters used
- Cost per mile = gallons x price / miles
Worked example
You drive 350 miles and the next fill-up takes 12.5 gallons. Your fuel economy is 350 / 12.5 = 28.0 miles per gallon. In metric units, 350 miles is 563.3 km and 12.5 gallons is 47.3 liters, so the car uses 8.40 liters per 100 km, or 11.9 km per liter. At $3.50 per gallon the fuel cost is 12.5 x 3.50 = $43.75, which is $0.125 per mile.
To get a steady figure, track three or four tanks and average them. A single tank can swing by several percent because pumps shut off at different points. If your figure drops suddenly, check tire pressure first, then look at brakes, filters and driving habits.
Assumptions & limits
- The tank is filled to the same level at both fill-ups. Different pumps and different fill levels can shift one reading by several percent.
- Uses US gallons. Imperial gallons are larger, so UK figures will not match.
- The cost per mile counts fuel only, not maintenance, insurance or depreciation.
- City and highway driving give different figures, so average several tanks that match how you drive.
- For an electric vehicle, use the EV vs Gas Cost Calculator, which handles kilowatt-hours.
Frequently asked questions
How do I calculate MPG?
Divide the miles you drove by the gallons of fuel you used. 350 miles on 12.5 gallons is 28 miles per gallon.
How do I convert MPG to L/100 km?
Divide 235.215 by the mpg figure. 28 mpg is 8.40 L/100 km.
Why is my real MPG lower than the sticker?
Speed, load, weather, short trips and driving style all change fuel economy. Sticker figures come from standard tests.
How often should I check my MPG?
Many drivers check every few fill-ups. A sudden drop can point to tire pressure, a dragging brake or an engine problem.
What is a good MPG?
It depends on the vehicle type. Compare with similar vehicles, since a truck and a compact car have different ranges.
Does the calculator use US or imperial gallons?
US gallons. A US gallon is about 3.785 liters.
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Last updated: November 2026