Road Trip Gas Cost Calculator
Planning a road trip and want to know how much you will spend on gas? This calculator takes three simple inputs: the distance you plan to drive, your vehicle's fuel economy in miles per gallon (MPG), and the current price per gallon of fuel. It divides the distance by your MPG to find gallons needed, then multiplies by the gas price to give your total fuel cost. Use the EPA's fueleconomy.gov to find your vehicle's official MPG rating, and the EIA's weekly gas price data for current regional prices.
Gas cost formula
Gallons needed = Distance / MPG
Total fuel cost = Gallons * Price per gallon
For 300 miles at 28 MPG: 300 / 28 = 10.71 gallons. At $3.50/gallon: 10.71 * $3.50 = $37.50.
Tips for reducing fuel costs on a road trip
- Maintain steady highway speeds. Fuel economy drops sharply above 50 mph; every 5 mph over 50 costs roughly 7% to 14% more in fuel (EPA estimate).
- Keep tires inflated to the manufacturer's recommended pressure. Under-inflated tires reduce MPG by up to 3%.
- Remove unnecessary cargo weight. An extra 100 lb reduces MPG by about 1% in typical vehicles.
- Use cruise control on flat terrain to maintain consistent speed.
- Plan fuel stops using GasBuddy or the EIA weekly price map to find cheaper stations along your route.
Road trip gas cost: frequently asked questions
How is road trip gas cost calculated?
Gas cost equals the trip distance divided by your vehicle's fuel economy (MPG), which gives gallons needed. Multiply gallons by the price per gallon to get the total fuel cost. For example, 300 miles at 28 MPG needs 10.71 gallons. At $3.50/gallon that is $37.50.
Where can I find the current gas price near me?
The U.S. Energy Information Administration (EIA) publishes weekly average retail gasoline prices by region at eia.gov. AAA also publishes daily national and state averages at gasprices.aaa.com.
Does this account for city vs highway driving?
This calculator uses a single MPG figure. For a mixed drive, use your vehicle's combined MPG rating, which the EPA lists on fueleconomy.gov. For a mostly highway trip use the highway MPG; for city driving use the city MPG.
How do I find my car's MPG rating?
The U.S. EPA fuel economy guide at fueleconomy.gov lists official city, highway, and combined MPG for every vehicle sold in the US. You can also calculate your actual MPG by dividing miles driven by gallons used from your last fill-up.
Can I use this for a round trip?
Yes. Simply enter double the one-way distance in the distance field to get the round trip fuel cost. Alternatively, calculate the one-way cost and multiply by two.
Official sources
- U.S. EPA Fuel Economy Guide: fueleconomy.gov.
- U.S. Energy Information Administration, weekly retail gasoline prices: eia.gov/petroleum/gasdiesel.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.