How to use the MPG calculator
Divide miles driven by gallons used. For a useful real-world estimate, measure across a full tank or several fill-ups rather than a very short drive.
MPG formula
The calculator also shows gallons per 100 miles, which can make fuel consumption easier to compare because lower values are better.
Example: Isaac measures fuel economy
Isaac fills the tank, drives 360 miles, and needs 12 US gallons to refill to the same level. His measured fuel economy is 360 ÷ 12 = 30 MPG.
Using consistent fill levels improves the comparison. Several full-tank measurements can give a more representative average than one short trip.
Measure fuel used between comparable fill-ups
Drive 300 miles and refill with 10 US gallons: fuel economy is 30 MPG. Using full-to-full tank measurements makes the comparison more consistent.
US and imperial gallons differ. This calculator uses US gallons, so convert an imperial-gallon quantity before entering it.
Convert US MPG to liters per 100 kilometers
For US gallons, liters per 100 kilometers equals 235.214583 divided by MPG. A vehicle achieving 30 US MPG uses about 7.84 liters per 100 kilometers. Higher MPG and lower liters per 100 kilometers both mean less fuel used per distance.
US and imperial gallons have different volumes, so identical MPG figures on those two scales do not mean identical fuel economy. This calculator uses US gallons.
Assumptions and limitations
What the estimate assumes
Pump shutoff differences, idling, driving conditions, and incomplete fill-ups can affect tank-to-tank measurements.
MPG Calculator FAQs
How do I measure MPG accurately?
Fill the tank, reset the trip odometer, drive normally, then refill and divide the miles driven by the gallons added.
Is higher MPG better?
Yes. Higher MPG means more miles traveled per gallon of fuel.
What is gallons per 100 miles?
It is the number of gallons needed to travel 100 miles. Lower is better.
Does weather affect MPG?
Yes. Temperature, traffic, speed, wind, terrain, tire pressure, and vehicle load can all affect real-world fuel economy.
Why does my calculated MPG differ from the car display?
Vehicle displays use onboard estimates, while a fill-up calculation depends on pump volume and trip distance. Differences in measurement and driving conditions can produce different results.
Measured fuel economy can vary from official ratings and from one tank to the next.