MPG Calculator

How to measure your own MPG

The most reliable way is the fill-to-fill method. Next time you fill the tank, reset your trip odometer to zero (or write down the total odometer reading). Drive normally until you need to fill up again, then note how many gallons it took to fill the tank, that's your gallons used. The distance shown on your trip odometer since the last fill is your miles driven. Enter both numbers here and the calculator divides miles by gallons to give you MPG.

For a more stable number, do this over a full tank rather than a partial fill, and repeat it over a few tanks if your driving varies a lot week to week (mostly highway one week, mostly stop-and-go city driving the next). A single fill-up during unusually cold weather or a trip with a fully loaded car will read differently than your normal average, so one tank is a data point, not necessarily your true average.

Worked example

Say you drove 350 miles since your last fill-up, and it took 11.5 gallons to top the tank back off. 350 divided by 11.5 comes out to 30.43 mpg. Add a gas price of $3.50 a gallon and the calculator also shows $0.115 per mile, or $11.50 per 100 miles, a handy number for comparing two cars, or for budgeting a longer drive without switching over to the trip cost calculator.

Why your MPG might differ from the EPA sticker number

The EPA rating on a new car's window sticker comes from standardized lab testing, not from driving on real roads, so it's normal for your actual number to land a bit above or below it. The biggest factors that pull your real MPG away from the sticker number:

• City driving with lots of stop-and-go traffic burns noticeably more fuel per mile than steady highway cruising.
• Cold weather thickens engine oil and takes longer to reach an efficient operating temperature, which hurts short trips especially.
• Aggressive acceleration and hard braking waste fuel that steady, gradual driving does not.
• Extra weight in the car (cargo, roof boxes, a full load of passengers) takes more energy to move.
• Underinflated tires increase rolling resistance and quietly cost you mpg over time.
• Highway speeds above roughly 60-65 mph increase wind resistance sharply, which is why mpg often drops noticeably the faster you go above that range.

How many fill-ups should I average together?

One fill-up gives you a quick number, and that is fine for a rough check. But if your driving pattern varies a lot from week to week, three or four fill-ups averaged together give a much more representative picture of your everyday mpg than any single tank. Keep a simple running note (miles and gallons per fill-up) for a month, add up the total miles, add up the total gallons, and divide the two totals instead of averaging four separate mpg numbers; that gives a more accurate combined figure than averaging the per-tank results, because it naturally weights longer tanks more heavily, which is the mathematically correct way to combine rates like this.

Not sure what to expect for your type of vehicle?

If you want a ballpark figure before you've logged a real fill-up, see the average gas mileage by vehicle type reference for typical mpg ranges by compact car, sedan, SUV, pickup truck and hybrid. Once you have a real number from this calculator, plug it into the gas cost calculator to estimate what an upcoming trip will actually cost, including support for round trips and splitting the cost between passengers.

What this calculator does with your numbers

Miles driven, gallons used and the optional gas price never leave your browser; the division happens locally in JavaScript the moment you type. Nothing is uploaded, logged, or stored on a server anywhere. The only thing saved is your last entered values, in your own browser's local storage, purely so the page can remember them the next time you open it. See the privacy page for the full explanation of what is (and is not) collected on this site.