Gas Mileage Calculator
Calculate your vehicle's fuel economy in MPG from miles driven and gallons used.
Try an example
28 mpg
About this calculator
What Is Gas Mileage?
Gas mileage — fuel economy or fuel efficiency — tells you how far your vehicle travels on a given amount of fuel. In the U.S. it is expressed in miles per gallon (mpg); in much of the world it is liters per 100 kilometers (L/100 km) or kilometers per liter. Knowing your real mileage helps you budget for fuel, spot mechanical problems early and decide whether a different vehicle would save money. This gas mileage calculator works it out from the distance you drove and the fuel you used.
How to Measure Your Mileage
- Fill the tank completely and note the odometer reading, or reset the trip meter.
- Drive as you normally would until the tank is mostly empty.
- Fill up again to the same point and write down how much fuel it took.
- Divide the distance driven since the last fill-up by the fuel added: mpg = miles ÷ gallons.
For example, 360 miles on 12 gallons is 30 mpg. To convert to L/100 km, use 235.215 ÷ mpg, so 30 mpg is about 7.8 L/100 km. Averaging over several tanks smooths out the noise.
Worked Example
Driving 350 miles on 12.5 gallons of gas works out to 28 mpg — equivalent to about 8.4 liters per 100 km.
How to Improve Gas Mileage
- Choose an efficient vehicle. All-wheel-drive and four-wheel-drive models generally use more fuel than front- or rear-wheel drive, since more of the drivetrain is working.
- Keep tires properly inflated. Under-inflated tires waste energy, costing roughly 0.3% in mileage for every PSI of pressure lost.
- Drive steadily. Avoid rapid acceleration and braking, and use cruise control on highways.
- Mind your speed. Most vehicles are most efficient between about 45 and 60 mph; wind resistance rises quickly above that.
- Cut weight and drag. Remove cargo you do not need and take off roof racks when not in use.
- Don't idle. Turn the engine off if you will be stopped for more than a minute or so.
- Keep up maintenance: clean filters, the right oil and good alignment all help.
Use Your Mileage to Plan
Once you know your real number, plug it into the Fuel Cost Calculator to price a trip, or check your travel time with the Speed Calculator. Different units of distance and volume are easy to switch with the Unit Conversion Calculator.
Worked example
Driving 350 miles on 12.5 gallons of gas works out to 28 mpg — equivalent to about 8.4 liters per 100 km.
Frequently asked questions
How do I measure gallons used accurately?
Fill the tank completely, reset your trip odometer, drive normally, then fill up again and note both the miles driven and the gallons needed to refill — that refill amount is what was actually used.
Why does my mileage vary between fill-ups?
City driving, highway driving, weather, tire pressure, and load all affect fuel economy — tracking mileage over several fill-ups gives a more reliable average than any single tank.
