Gas Mileage (MPG) Calculator
Calculate your car's actual fuel economy based on miles driven and gallons of gas used on a fill-up.
Getting an accurate fill-up measurement
For the most accurate result, fill your tank completely, reset your trip odometer (or note the current mileage), drive normally until your next fill-up, then fill up completely again and record both the miles driven and gallons needed to fill up. Using a partial fill-up introduces error, since you can't be certain exactly how much fuel was actually used.
Your actual MPG will typically vary from the manufacturer's advertised EPA estimate — real-world factors like driving style, terrain, weather, and whether you're mostly on highway or city streets all affect actual fuel economy, often meaningfully.
Why tracking your own MPG is useful
Comparing your calculated MPG over multiple fill-ups can reveal trends — a gradually declining MPG might indicate a maintenance issue (like worn spark plugs, low tire pressure, or a dirty air filter) worth investigating, since sudden or gradual drops in fuel economy are often an early warning sign.
Tracking MPG is also useful for realistically budgeting fuel costs for regular commutes or road trips, since it's based on your actual driving conditions rather than an idealized manufacturer estimate.
Frequently asked questions
Why is my actual MPG different from the EPA sticker estimate?
EPA estimates are based on standardized test conditions that don't fully reflect real-world driving — your actual MPG depends on driving style, terrain, weather, and the mix of highway versus city driving you actually do.
How can I get the most accurate MPG measurement?
Fill your tank completely, track the miles driven until your next fill-up, then fill up completely again and use that fuel amount — partial fill-ups introduce uncertainty into the calculation.