Estimating gas for a trip
Divide the distance by your car's fuel economy to get the fuel you will use, then multiply by the price. A 300-mile road trip in a car that gets 30 mpg uses 10 gallons; at $3.50 a gallon that is $35, or about 11.7 cents a mile.
Finding your fuel economy
The EPA window sticker and fueleconomy.gov list official city, highway and combined mpg for every car sold in the US. Your real number depends on how you drive: highway speeds above 60 mph, roof racks, cold weather and heavy loads all lower it. For the best estimate, fill the tank, reset the trip meter, and divide the miles driven by the gallons at the next fill-up.
Other units
- km/L (used in Brazil, India and Japan): a car doing 12 km/L over 500 km uses 41.7 L.
- L/100 km (Europe, Canada, Australia): 6.5 L/100 km over 300 km uses 19.5 L.
- UK mpg uses imperial gallons, which are 20% larger; convert to US mpg by multiplying by 0.833.
Remember to double the distance for a round trip and to split the total if you share the drive.
How this works
For mpg and km/L, the page divides the distance by the fuel economy to get the gallons or litres used; for L/100 km it multiplies the distance by the consumption and divides by 100. The cost is the fuel used times the price, and the cost per mile or km is the cost divided by the distance. Use US gallons with mpg.
Frequently asked
How do I calculate gas cost for a trip?
Miles ÷ mpg × price per gallon. 300 miles at 30 mpg and $3.50 a gallon is $35.
Where do I find my car's mpg?
On the EPA window sticker, on fueleconomy.gov, or by measuring miles per tank yourself.
Should I use city or highway mpg?
Use highway for road trips and combined for mixed driving.
Does this work for diesel or electric cars?
Diesel, yes. For electric cars use the electricity cost calculator with kWh per mile.
Sources
Reviewed Oct 17, 2026 · test vectors fixtures/calculators/everyday/fuel-cost-calculator/