Fuel Cost Calculator

To calculate gas mileage, fill your tank completely and reset your trip odometer to zero. Drive normally until you need to refuel, then divide the number of miles traveled by the number of gallons of gas it took to refill the tank. For example, if you drove 350 miles and it took 14 gallons to fill up, your gas mileage is 350 ÷ 14 = 25 miles per gallon (MPG). Repeat over a few fill-ups and average the results for a more reliable number, since short trips and cold starts can temporarily lower the reading.

To estimate the fuel cost of a trip, divide the total distance by your vehicle's fuel efficiency (MPG) to get the gallons of gas needed, then multiply that by the current price per gallon. For a 300-mile trip in a car that gets 25 MPG at $3.50 per gallon: 300 ÷ 25 = 12 gallons, and 12 × $3.50 = $42.00 total fuel cost. Check current local gas prices before a long trip since prices can vary significantly by region and by gas station.

A good MPG depends on the vehicle type: compact and midsize sedans typically average 30–40 MPG on the highway, hybrids often reach 45–60 MPG, and full-size SUVs or trucks average 15–22 MPG. The EPA-rated combined average for new vehicles sold in the U.S. is around 25–28 MPG. Anything meaningfully above your vehicle class's average is considered good fuel economy, while a sudden drop in your own car's typical MPG can signal a maintenance issue like underinflated tires or a dirty air filter.

MPG and L/100km measure fuel economy in opposite directions — MPG is distance per unit of fuel, while L/100km is fuel used per fixed distance — so a direct multiplication doesn't work. The standard conversion is L/100km = 235.215 ÷ MPG (using US gallons and miles). For example, 25 MPG converts to roughly 235.215 ÷ 25 = 9.4 L/100km. Lower L/100km values mean better fuel efficiency, which is the opposite of MPG where higher is better.

If you track your fuel economy in metric units, L/100km = 100 × liters used ÷ kilometers driven. For example, if you used 24 liters of fuel to drive 300 km, your consumption is 100 × 24 ÷ 300 = 8.0 L/100km. This calculation works directly from your fill-up data without needing to convert from MPG first, which is why drivers in metric countries track fuel economy this way instead.

Keep tires inflated to the manufacturer's recommended pressure, since underinflated tires increase rolling resistance and can lower MPG by several percent. Avoid aggressive acceleration and braking, remove excess weight and roof cargo boxes, use cruise control on the highway, and keep up with regular maintenance like air filter and spark plug changes. Combining errands into fewer trips and avoiding excessive idling also meaningfully improve real-world fuel economy over time.