Road Trip Fuel Cost Calculator
Estimating fuel costs is one of the first steps in planning a road trip budget. This calculator applies the standard US Department of Energy formula: divide the total distance by your vehicle's fuel economy to get gallons used, then multiply by the current gas price to get the total fuel cost. It also shows cost per mile and the number of gallons needed so you can plan refuelling stops.
Fuel cost formula (US DOE standard)
Gallons used = Distance (miles) / Effective MPG
Fuel cost = Gallons used x Price per gallon x Number of vehicles
Effective MPG = Rated MPG / (1 + Buffer / 100)
The US Department of Energy uses this formula in its fuel savings calculator and vehicle comparison tools. The real-world efficiency buffer reduces the rated MPG to account for acceleration, air conditioning, elevation, and cargo weight, which typically reduce real-world economy 5% to 20% below the EPA sticker rating.
Tips for reducing road trip fuel costs
- Maintain highway speeds of 55 to 65 mph; fuel economy drops approximately 7% to 14% at 70 mph compared to 55 mph (US DOE data).
- Keep tyres inflated to the manufacturer's recommended pressure (printed inside the driver's door jamb). Under-inflation reduces fuel economy by approximately 0.2% per PSI below optimal.
- Remove roof racks and cargo carriers when not in use; they can reduce fuel economy by 2% to 8% at highway speeds.
- Use cruise control on flat highway sections to maintain steady speed and reduce unnecessary acceleration.
- Plan refuelling stops using apps that show real-time gas prices to avoid high-markup stations in remote areas.
Road trip fuel cost calculator: frequently asked questions
How do I calculate fuel cost for a road trip?
Fuel cost = (Distance / Fuel economy) x Price per gallon. For example, a 500-mile trip in a vehicle that gets 30 MPG at $3.50 per gallon costs (500 / 30) x $3.50 = $58.33 in fuel. This calculator uses the same standard formula used by the US Department of Energy.
What is a typical fuel economy for a car?
According to the US EPA, the average fuel economy of model year 2023 light vehicles was approximately 26.4 MPG combined. Compact cars typically achieve 30 to 40 MPG. SUVs and trucks typically achieve 18 to 26 MPG. Hybrids achieve 45 to 60 MPG. Electric vehicles are measured in MPGe (miles per gallon equivalent) and use a separate cost calculation based on kWh per mile.
How do I find the current gas price?
The US Energy Information Administration (EIA) publishes weekly average retail gasoline prices by region and state at eia.gov. The national average regular unleaded price is updated every Monday. Use the current price for your departure state for the most accurate estimate.
Should I budget for more fuel than calculated?
Yes. Real-world fuel economy is often 5% to 20% lower than the EPA rated figure due to factors including highway speed, air conditioning, cargo weight, elevation gain, and driving style. Adding a 10% to 15% buffer to the calculated fuel cost is recommended for road trip planning.
Can I use this for metric (litres per 100 km)?
This calculator uses US units (miles, gallons, USD). For metric fuel cost: Total litres = Distance (km) x Fuel consumption (L/100km) / 100. Fuel cost = Total litres x Price per litre.
Official sources
- US Department of Energy, fuel economy and driving tips: fueleconomy.gov driving habits.
- US Energy Information Administration, weekly retail gasoline prices: eia.gov gas and diesel prices.
- US EPA, fuel economy labelling: epa.gov fuel economy.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.