π MPG Calculator
Real-world fuel economy from your fill-ups, plus trip cost estimates.
Your fuel economy
How to Use the MPG Calculator
Two modes. Fill-up mode takes miles driven and gallons pumped and gives your true MPG plus cost per mile. Trip mode takes distance, your MPG, and gas price and estimates fuel cost before you leave. Both use US gallons and honest division, no lab-test optimism.
For your MPG: fill the tank, reset the trip odometer, drive, fill again, and enter miles and gallons.
Add the gas price to get cost per mile alongside MPG.
For a trip: switch modes, enter distance, your measured MPG, and gas price for the fuel budget.
How MPG Math Works
Fuel economy is one division, but the inputs must be honest: miles between two full tanks divided by the gallons it took to refill. Partial fill-ups corrupt the math, so always measure full-to-full. Cost per mile falls out immediately once MPG is known, and it is the number that actually governs your wallet.
Worked example, verified: 320 miles on 12.5 gallons. MPG: 320 Γ· 12.5 = 25.6. At $3.50 a gallon, cost per mile: 3.50 Γ· 25.6 = $0.1367, about 13.7 cents. Trip version: 600 miles at 28 MPG needs 21.43 gallons; at $3.50 that is $75.00. In metric: 25.6 MPG = 235.2 Γ· 25.6 = 9.19 L/100km.
Why Your MPG Misses the Sticker
The EPA number comes from a laboratory driving cycle, and your life is not a laboratory. Short trips are the biggest thief: a cold engine runs rich until it warms up, so a two-mile errand can return half the rated economy. Idling gets zero miles per gallon by definition, and drive-throughs, school lines, and remote-start warmups add up. Speed is next: drag grows with the square of velocity, and economy typically drops sharply past 65 mph. Underinflated tires, a loaded roof box, and winter-blend gasoline each take their cut. A 10 to 20 percent gap between sticker and reality is normal physics, not a defective car. A 40 percent gap is a maintenance issue: check tire pressure first, then the air filter, then for a stuck brake caliper.
Cost Per Mile: The Number That Matters
MPG is for bragging; cost per mile is for budgeting. At $3.50 a gallon, a 25 MPG car costs 14 cents a mile in fuel while a 40 MPG hybrid costs under 9 cents. Over 13,500 miles a year (roughly the US average), that gap is about $700 annually, which is the honest way to evaluate a hybrid premium. Cost per mile also settles drive-vs-fly debates: multiply by trip miles, add tolls and parking, and compare against the airfare. Fuel is only part of true driving cost (the IRS standard mileage rate, 70 cents a mile for 2026, bundles depreciation, insurance, and maintenance), but fuel is the part you control trip to trip.
Tips for Better Real-World MPG
Drive like there is an egg under the gas pedal: gentle acceleration and early coasting beat every gadget. Keep tires at the door-jamb pressure, checked monthly, since every missing PSI costs a fraction of a percent. Lose the roof box when the trip ends; it is a parachute. Combine short errands into one warmed-up loop. Use cruise control on flat highways but take over on hills, where a smart foot beats a dumb cruise. And track a month of fill-ups before changing anything. You cannot improve a number you have not measured, and the calculator above is the fastest way to start.
Worked Example: The Hybrid Commute
A hybrid commuter drives 520 miles on 11.2 gallons: 520 / 11.2 = 46.4 MPG. At $3.60 a gallon, cost per mile is 3.60 / 46.4 = $0.0776, about 7.8 cents. Monthly at 1,200 miles: 1,200 x 0.0776 = $93.10 in fuel. The old car did 22 MPG: 3.60 / 22 = $0.1636 per mile, $196.36 a month. The hybrid saves $103.26 a month, $1,239 a year, which is the number to weigh against any hybrid price premium.
Trip version for the same car: 400 miles at 46.4 MPG needs 8.62 gallons; at $3.60 that is $31.03. The whole weekend trip costs less than one tank in the old car.
The Dashboard MPG Lie
Dashboard fuel-economy displays read optimistic, typically 5 to 10 percent high. Manufacturers calibrate them from injector pulse data rather than measured fuel flow, and the calibration errs generous. A dash reading 32 MPG often hand-calculates to 29 or 30. This is not a conspiracy; it is just a less precise measurement presented with too many significant digits.
The hand calculation is the truth: miles between full tanks divided by gallons to refill. Track it for a month and you will know your real number, which is the one that belongs in every other calculation on this page. Trust the pump and the odometer. The dashboard is entertainment.
Worked Example: 380 Miles on 12.4 Gallons
Fill up, drive 380 miles, fill up again with 12.4 gallons. MPG = 380 / 12.4 = 30.6. Run three tanks the same way: 30.6, 31.2, 29.8, averaging 30.5. That is your real number, better than the dashboard's optimistic 32. At $3.50 per gallon, cost per mile = 3.50 / 30.5 = 11.5 cents. A 1,000-mile month costs $115 in fuel, a number worth knowing before choosing between two cars.
Compare against the sticker: the EPA combined rating for this car is 33 mpg. Missing it by 2.5 mpg is normal; EPA tests run at moderate speeds with no air conditioning, while real life includes 75-mph highways and summer AC. If you beat the sticker, you drive gently; if you miss it by 20 percent, check tire pressure and the air filter before blaming the car.
Why Your MPG Misses the Sticker
Speed is the biggest factor. Fuel economy peaks around 50 to 55 mph for most cars and falls roughly 15 percent by 75 mph, because aerodynamic drag grows with the square of speed. Short trips murder mpg too: a cold engine runs rich for the first few miles, so a 3-mile commute can return half the highway number. Idling gets zero mpg by definition, and remote-start warmups in winter are pure fuel burn for comfort.
Tires are the quiet thief. Underinflation by 5 PSI costs 2 to 3 percent in fuel economy and wears the shoulders; the door-jamb sticker gives the right pressure, not the tire sidewall maximum. Roof racks and open windows at highway speed add drag that shows up directly in the per-tank math. Fix the cheap things first: pressure, filter, and speed discipline recover more mpg than any gadget.
Cost Per Mile: The Number That Matters
MPG is abstract; cents per mile decides purchases. Car A at 25 mpg and Car B at 35 mpg, gas at $3.60: A costs 14.4 cents per mile, B costs 10.3 cents. Over 12,000 miles a year the gap is $492. Over a 150,000-mile ownership it is $6,150, which often exceeds the price premium of the efficient car. Run the calculator with your actual annual mileage and local gas price before deciding the thirstier car is "cheaper."
Frequently Asked Questions
How do I calculate my MPG?
Fill the tank, reset the trip odometer, drive normally, then fill up again. Divide miles driven by gallons used: 320 miles Γ· 12.5 gallons = 25.6 MPG. The calculator above does the division and adds cost-per-mile when you enter the gas price.
What is a good MPG for a car?
For 2026 model-year US vehicles, the mid-20s is typical for gasoline cars, low-30s for efficient sedans and hybrids, and high-30s to 50+ for dedicated hybrids. Trucks and large SUVs often land in the high teens. Compare your computed MPG against your car's EPA sticker, not against other people's cars.
Why is my actual MPG lower than the EPA rating?
EPA tests run in a lab on fixed cycles; real life adds short trips, cold starts, idling, cargo, hills, and highway speeds above 65 mph. A 10 to 20 percent shortfall is normal. If the gap is much bigger, check tire pressure, air filters, and whether the car needs service.
How do I calculate fuel cost for a road trip?
Divide trip miles by your MPG, then multiply by the gas price. A 600-mile trip at 28 MPG uses 21.4 gallons; at $3.50 a gallon that is $75. The calculator's trip mode does this in one step.
What is cost per mile and why does it matter?
Your fuel cost divided by miles driven: gas price Γ· MPG. At $3.50 a gallon and 25 MPG, every mile costs 14 cents in fuel. Cost per mile lets you compare cars honestly and decide whether driving or flying wins for a trip.
Does premium gas improve MPG?
Only if your engine is designed for it. Cars that require premium can knock and lose efficiency on regular, but cars designed for regular gain nothing from premium. Check the owner's manual: requires means requires, recommends is optional.
How much does speeding hurt fuel economy?
A lot past 60 mph. Aerodynamic drag rises with the square of speed, so fuel economy typically falls fast above 65. The old rule of thumb still holds: every 5 mph over 50 is like paying extra per gallon. Cruise control on flat highways is the cheapest speed control you own.
Do I need to track every fill-up?
For one accurate number, two consecutive fill-ups are enough. For a trustworthy average, track a month; individual tanks vary with driving mix. Apps that log odometer and gallons do the same math as this calculator automatically.
How is MPG different from liters per 100 km?
They are inverses. MPG is distance per fuel (higher is better); L/100km is fuel per distance (lower is better). Convert: 235.2 Γ· MPG = L/100km. So 25.6 MPG is about 9.2 L/100km. The calculator reports both.