Work out your real MPG the way drivers actually measure it — two odometer readings and the gallons that went in. Then see what a mile costs and what a year of fuel adds up to.
A gas mileage calculator works out your real fuel economy the way drivers actually measure it: fill the tank to the brim, note the odometer, drive, refill, then divide the miles between the two readings by the gallons that went in. It is the honest number behind the EPA window sticker — which is measured on a lab cycle and is typically 10–15% optimistic. The calculator also converts MPG to L/100km, gives your fuel cost per mile and per 100 miles, shows how far a full tank gets you, and totals your fuel spend over a year.
MPG = miles driven ÷ gallons used. Cost per mile = (gallons × price per gallon) ÷ miles. Yearly cost assumes 12,000 miles at $3.50/gal.
| Vehicle | Miles driven | Gallons used | MPG | Cost per mile | Yearly fuel cost |
|---|---|---|---|---|---|
| Compact sedan (e.g. Civic) | 312 | 9.6 | 32.5 | $0.108 | $1,292 |
| Midsize sedan (e.g. Camry) | 300 | 11.11 | 27.0 | $0.130 | $1,555 |
| Compact SUV (e.g. RAV4) | 300 | 13.64 | 22.0 | $0.159 | $1,910 |
| Full-size pickup (e.g. F-150) | 300 | 16.67 | 18.0 | $0.194 | $2,334 |
| Hybrid sedan (e.g. Prius) | 400 | 8.89 | 45.0 | $0.078 | $933 |
| Plug-in hybrid (60 mpg-equiv) | 400 | 6.67 | 60.0 | $0.058 | $700 |
Reference: U.S. DOE / EPA FuelEconomy.gov. Real-world MPG is usually 10–15% below the EPA window-sticker rating, and city driving worse than that.
32.5 mpg
7.2 L/100km over 312 miles
$0.11/mi
$10.77 per 100 miles
488 mi
$1,292.31
369 gal over 12,000 miles
MPG = miles driven ÷ gallons used. L/100km = 235.215 ÷ mpg. Fill-ups taken at the same pump and the same fuel grade give the most accurate reading; a tank topped off part-way first understates your MPG.
| MPG | Gallons/year | Cost/year | Cost/mile |
|---|---|---|---|
| 20 mpg | 600 | $2,100.00 | $0.18 |
| 25 mpg | 480 | $1,680.00 | $0.14 |
| 30 mpg | 400 | $1,400.00 | $0.12 |
| 35 mpg | 343 | $1,200.00 | $0.10 |
| 40 mpg | 300 | $1,050.00 | $0.09 |
| 45 mpg | 267 | $933.33 | $0.08 |
| 50 mpg | 240 | $840.00 | $0.07 |
Each extra 5 mpg saves between $93 and $420 a year at 12,000 miles and $3.50/gal — the less efficient the car, the more the improvement is worth.
Cross-checked against authoritative formulas (IRS, NIST, ACSM) and updated for 2025/2026 tax years and rates.
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FAQ
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A gas mileage calculator works out your real fuel economy from your own fill-up records: the miles you drove between two full tanks, divided by the gallons that went into the second one. It is the number you actually get, as opposed to the EPA window-sticker rating, which is a lab figure. The calculator also gives you cost per mile, the range on a full tank, and what a year of fuel costs at your annual mileage.
How it works
Our gas mileage calculator works out your real fuel economy from two odometer readings and the gallons used to refill, then converts it to cost per mile, tank range and yearly fuel cost.
Fill the tank to the brim and write down the odometer reading. Note the mileage on the pump — most pumps reset it at the fill-up, which is exactly the number you want.
Drive normally until you refill the same tank, then record the new odometer reading and the gallons the pump put in. For the most accurate result, fill to the same level both times and use the same fuel grade.
Type both odometer readings, the gallons used, the price per gallon, your tank size and your annual mileage into the gas mileage calculator. It subtracts the odometer readings and does the division for you.
The gas mileage calculator shows your MPG and the L/100km equivalent, your fuel cost per mile and per 100 miles, how far a full tank gets you, and what you spend on fuel over a year. A reference table below shows yearly fuel cost at common fuel economies.
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