Estimate how much a road trip or your daily commute costs in gas.
Trip fuel cost depends on three variables: distance, vehicle fuel efficiency, and fuel price. Divide the trip distance by your vehicle's miles per gallon (MPG) to get gallons needed, then multiply by the price per gallon. A vehicle averaging 28 MPG on a 500-mile trip uses about 17.9 gallons. At $3.40 per gallon, the trip costs roughly $61. This calculator supports both U.S. (MPG, gallons, dollars) and metric (L/100km, liters) units.
The EPA rates vehicles with separate city, highway, and combined MPG figures. Highway driving is more fuel-efficient because engines operate closer to their optimal RPM range and there is less braking and accelerating. City driving can use 20 to 40% more fuel per mile than highway driving. For long road trips, use the highway MPG rating. For mixed commuting, the combined rating is more accurate. Real-world fuel economy often comes in 10 to 15% below EPA estimates due to driving habits, weather, and vehicle condition.
Speed has a significant effect on highway fuel economy. Most vehicles achieve peak efficiency between 35 and 55 mph. Above 55 mph, aerodynamic drag increases with the square of speed, so fuel economy drops noticeably. The Department of Energy estimates that every 5 mph above 50 mph is roughly equivalent to paying an additional $0.20 to $0.30 per gallon of gas at 2025 prices.
Changing tire sizes? The Tire Size Calculator checks speedometer accuracy and fitment for new tire sizes.
Tire pressure is one of the simplest factors to control. Underinflated tires increase rolling resistance and can reduce fuel economy by 1 to 3%. Aggressive driving (rapid acceleration and hard braking) can lower gas mileage by 15 to 33% at highway speeds and 10 to 40% in stop-and-go traffic, according to the Department of Energy. Excess cargo weight also matters: every 100 extra pounds in the vehicle reduces MPG by about 1 to 2% for passenger cars.
Cold weather reduces fuel economy because engines take longer to reach efficient operating temperature, tire pressure drops, and winter-blend gasoline has slightly less energy per gallon. Air conditioning use in hot weather can reduce fuel economy by more than 25% on short trips. For a broader trip planning tool that includes fuel stops and drive time, see the Road Trip Calculator.
Fuel efficiency varies significantly based on driving conditions. Highway driving is typically 15 to 30% more efficient than city driving due to fewer stops, starts, and idling periods. Aggressive driving (rapid acceleration, hard braking, speeding) can reduce fuel economy by 15 to 33% on the highway and 10 to 40% in the city, according to the U.S. Department of Energy. Tire pressure is a commonly overlooked factor: properly inflated tires improve fuel economy by up to 3%. Additional factors include vehicle weight (every 100 extra pounds reduces MPG by about 1%), air conditioning use (can reduce fuel economy by more than 25% in certain conditions), and engine maintenance (a properly tuned engine can improve MPG by 4%). For electric vehicles, equivalent efficiency is measured in miles per kWh rather than miles per gallon.