How the Gas Calculator works
This tool estimates the fuel a trip will burn and what it will cost, using the same arithmetic drivers use every day: distance, fuel economy, and the price of gas. Enter your trip distance, your vehicle's miles-per-gallon (MPG) rating, and the current price per gallon, and the calculator returns the gallons you'll need, the total cost, the cost per mile, and — if you're sharing the drive — the cost per person.
The formula
The math behind every result is simple division and multiplication:
- Total distance = trip distance, doubled automatically if you select "Round trip."
- Gallons needed = total distance ÷ vehicle fuel economy (MPG).
- Total gas cost = gallons needed × price per gallon.
- Cost per mile = total gas cost ÷ total distance.
- Cost per person = total gas cost ÷ number of people splitting the cost.
Where to find your fuel economy number
Your vehicle's official MPG rating is on its window sticker (for new cars) or the EPA's fueleconomy.gov database, and most modern dashboards also display a real-time or trip-average MPG. Combined MPG (a blend of city and highway) is the best all-purpose figure; use highway MPG for trips that are mostly interstate driving and city MPG for stop-and-go routes, since highway economy is typically higher than city economy.
Practical context
This estimate assumes steady fuel economy at your entered MPG figure and a constant price per gallon for the whole trip. Real-world mileage varies with speed, terrain, load, tire pressure, and traffic, and gas prices can differ from state to state or station to station. Use the result as a planning estimate, and re-run it with your dashboard's actual trip MPG once you're partway through a long drive for a more precise figure.