Gas Mileage Calculator

How it works

MPG = miles driven ÷ gallons refilled · L/100 km = 235.21 ÷ MPG · km/L = MPG × 0.4251 · UK MPG = MPG × 1.201 · cost per mile = fuel cost ÷ miles · average over a log = total miles ÷ total gallons

The fill-up method: top the tank until the pump clicks off, note the odometer (or reset the trip meter), drive normally, then refill to the click. The fuel the second fill takes is exactly what those miles used, so miles ÷ gallons is your true MPG. You can type the trip distance, two odometer readings, or a whole log of fill-ups — the log is the most reliable, because single tanks wobble with pump shut-off points and parking slopes. The overall average divides total distance by total fuel, which weights each tank by how much fuel it used; simply averaging the per-tank MPG figures over-weights short tanks. Results come in US MPG, litres per 100 km (lower is better), kilometres per litre and UK MPG (the imperial gallon is 20% bigger, so UK figures are 20% higher for the same car). Add your yearly mileage to see what a year of fuel costs and how much a few MPG would save, and the sticker rating to see how your driving compares. CO₂ uses the EPA figures of 8,887 g per gallon of gasoline and 10,180 g per gallon of diesel.

Worked example

320 miles on an 11.5-gallon refill is 320 ÷ 11.5 = 27.8 MPG — the same as 8.5 L/100 km, 11.8 km/L or 33.4 UK MPG. At $3.50 per gallon that works out to $0.126 per mile, or $12.58 per 100 miles, and the tank cost $40.25. Driving 12,000 miles a year at that rate uses about 431 gallons, roughly $1,509 of fuel and 3.8 tonnes of CO₂. A three-tank log of 320/11.5, 298/10.9 and 335/12.2 averages 953 ÷ 34.6 = 27.5 MPG.

Sources: fueleconomy.gov — Fuel economy guide and tips (US DOE / EPA) · US EPA — Greenhouse gas emissions from a typical passenger vehicle

Frequently asked questions