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 →If you're driving an electric vehicle, the math works differently. Instead of MPG and gas price, you're working with miles per kWh and electricity cost. Most EVs average 3–4 miles per kWh. At the national average electricity rate of around $0.17/kWh, a 600-mile road trip in an EV costs roughly $25–$34 — compared to $68 in a 30 MPG gas car at $3.40/gallon.
The catch: on a road trip, you'll likely be using DC fast chargers rather than home charging, and fast charging rates are significantly higher — often $0.30–$0.50/kWh. That brings EV road trip costs closer to, and sometimes above, gas cars depending on the route and charger availability.
If your road trip involves multiple legs — say, driving from Dallas to Denver to Salt Lake City and back — calculate the fuel cost for each segment separately. This is more accurate than treating the whole trip as a single distance, especially if you'll be driving through varied terrain (flat plains vs. mountain passes) that affects your actual MPG.
Add 10–15% to your total estimate as a buffer. You'll likely stop more than planned, take detours, or hit unexpected traffic. The buffer also accounts for searching for parking in cities, which means more idling.
Gas prices fluctuate week to week, and a $0.50/gallon swing can meaningfully change your budget on a long trip. On a trip requiring 50 gallons total, the difference between $3.00/gallon and $3.50/gallon is $25. Check current national average prices and prices in the states you'll be driving through before you finalize your budget.
Enter your route distance, MPG, and current gas price for a precise cost breakdown.
Road Trip Cost Calculator →