Before you hit the highway, it's worth knowing roughly what you'll spend on gas. The math is simple, and knowing your estimate in advance helps you budget smarter — and avoid surprise stops at expensive stations.
Road trip fuel cost comes down to three numbers: the distance you're driving, your car's MPG, and the current gas price.
Fuel Cost = (Miles ÷ MPG) × Gas Price per Gallon
For example: a 600-mile trip in a car that gets 30 MPG, with gas at $3.40/gallon:
That's it. The hard part is knowing your real-world MPG — not the EPA estimate on the window sticker.
EPA ratings are tested under controlled conditions. Highway driving at 75+ mph, AC on, and a loaded trunk will drop your MPG by 10–20% versus the official figure. If your car is rated at 35 MPG highway, assume 30–32 for planning purposes on a real road trip.
To find your real MPG: fill your tank, reset the trip odometer, drive normally, then divide miles driven by gallons used at your next fill-up.
Fuel efficiency drops significantly above 60 mph. Driving at 75 mph instead of 60 mph can reduce your MPG by 15–20%. On a long trip, slowing down by 10 mph can save you a noticeable amount of fuel.
Running the air conditioner adds roughly 5–15% to fuel consumption. In hot climates, this is unavoidable — just factor it in.
Every extra 100 lbs reduces fuel economy by about 1%. A fully loaded minivan will burn noticeably more than the same van with just the driver.
Mountain driving burns significantly more fuel than flat highway driving. If your route crosses mountain passes, add 10–20% to your estimate.
Gas prices vary by state and even by exit. California and Hawaii consistently have the highest prices; states like Texas, Oklahoma, and Mississippi tend to be cheapest. GasBuddy is a good tool for checking prices along your route before you leave.
Don't forget to double your calculation if you're driving back the same route. It sounds obvious, but it's easy to overlook when budgeting.
Using 30 MPG and $3.40/gallon as a baseline:
Adjust up or down based on your car's actual MPG and local gas prices.
Enter your route distance, MPG, and current gas price for a precise cost breakdown.
Road Trip Cost Calculator →