How to Actually Estimate a Road Trip’s Fuel Cost
Road trip fuel cost comes down to three numbers: total distance, average miles per gallon, and average price per gallon. The math is gallons used equals miles driven divided by mpg, then total cost equals gallons used times price per gallon. A 1,200 mile trip in a 28 mpg vehicle at $3.50 per gallon comes to 43 gallons and $150 in fuel. The math is easy. What people get wrong is the inputs.
The biggest input error is using the EPA highway mpg rating instead of your actual highway mpg. EPA numbers assume 60 mph cruising, flat terrain, no headwind, no air conditioning, no cargo, and a single driver. Real road trips have most of those working against you. If your car is rated 32 mpg highway and you cruise at 75 mph with luggage and AC, expect 25 to 27 mpg in reality. The calculator above lets you plug in your real-world number rather than the optimistic sticker number, which produces a much more honest cost estimate before you leave.
Why MPG Drops on Real Road Trips
Five things conspire against you on a typical road trip. Speed: aerodynamic drag rises with the square of velocity, so 75 mph costs 15 to 25 percent more fuel than 65 mph. Loaded vehicle: extra passengers, luggage, and cargo add weight, which raises rolling resistance roughly 1 to 2 percent per 100 pounds. Roof cargo: a loaded roof box can drop highway mpg by 10 to 20 percent at 70 mph because of disturbed airflow. Air conditioning: AC use costs 1 to 4 mpg depending on outside temperature and compressor sizing. Wind: a steady 15 mph headwind feels to the car like driving 15 mph faster than ground speed, costing roughly 8 to 12 percent in mpg.
The good news is that these are mostly under your control. Cruising 5 to 10 mph slower saves measurable fuel at zero risk. Packing in the cabin instead of on the roof saves more. Skipping the cargo box if you don’t really need it saves the most. None of these are deal-breakers — sometimes you need the extra cargo space and you have somewhere to be — but knowing the cost helps you decide whether to pay the toll or skip it.
Fuel Cost vs Total Trip Cost
Fuel is one line item in the real cost of a road trip. The other big ones are vehicle wear (tires, oil consumption, brake wear, depreciation by mile), tolls, lodging, food, and trip-related expenses (parking, ferries, attractions). The IRS standard mileage rate for 2026 is 70 cents per mile, which is meant to capture all vehicle operating costs including fuel, maintenance, depreciation, and insurance amortization. For a private road trip the actual marginal cost is usually 30 to 50 cents per mile, with fuel making up 10 to 18 cents of that.
The calculator above focuses on the fuel cost because that is the number that changes with your route choice, your driving speed, and the fuel price spread between cities. The other costs are roughly fixed regardless of whether you cruise at 65 or 75. Understanding the fuel cost helps you make smart trade-offs (drive an extra 50 miles for a $30 cheaper hotel? probably worth it). The other numbers stay the same either way.
Frequently Asked Questions
What mpg should I use for road trip planning?
Use your actual measured highway mpg from a previous trip if you have it. If not, take the EPA highway rating and subtract 10 to 15 percent for realistic conditions (75 mph cruising, AC, luggage, headwind). A vehicle rated 32 mpg highway typically delivers 27 to 29 mpg on a real road trip. For specific conditions like towing or roof cargo, expect another 10 to 20 percent reduction on top of that.
Does buying gas in cheaper states actually save money?
Sometimes, but less than you’d think. Going 25 miles off your route to save 30 cents per gallon on a 16 gallon fill-up saves $4.80 in fuel cost. The detour itself burns about $4 to $5 of fuel and takes 30 to 40 minutes. The savings are usually marginal. The real way to save on a road trip is to fill up just before crossing into expensive states (California, Hawaii, parts of the Northeast) when you can plan ahead.
How accurate are gas station apps for finding cheap fuel?
Generally accurate within 10 to 20 cents. GasBuddy, Waze, and Google Maps all pull crowdsourced price data that lags 1 to 24 hours behind reality. They are great for finding the cheapest station within a 5 to 10 mile radius. They are less reliable for prices an entire day’s drive away. Use them tactically (next fill-up) rather than strategically (whole trip planning).
Should I use cruise control to save fuel on a road trip?
On flat highways, yes. Cruise control holds a consistent throttle position and prevents the small accelerations a human driver makes unconsciously. The savings are usually 3 to 7 percent over a long highway run. On hilly terrain cruise control can be slightly worse than a skilled driver who eases off coming over crests, but modern adaptive cruise control handles hills well. For most road trips, leave it on once you’re on the freeway.
How much does towing a trailer increase fuel cost?
Significantly. Most vehicles lose 30 to 50 percent of their unloaded mpg when towing a typical trailer. A truck that gets 22 mpg empty often gets 12 to 15 mpg pulling a 6,000 lb travel trailer. Hilly terrain and headwinds make it worse. For trip planning, assume your mpg drops to roughly half of the empty figure if you’re pulling a substantial trailer. Camper vans built on truck chassis are similarly inefficient — about 12 to 18 mpg highway is typical.
Is it cheaper to drive or fly for a 1,000 mile trip?
Depends on the vehicle, fuel price, and number of travelers. A 1,000 mile trip in a 28 mpg car at $3.50/gallon costs $125 in fuel. Add wear and lodging (one or two nights on the road), and the all-in cost is $300 to $500. Round-trip economy flights for one person typically run $250 to $500 for that distance, plus airport parking and ground transport. For a family of four driving makes more financial sense by a wide margin. For solo travelers, flying and renting a car at the destination is often cheaper and dramatically faster.
How much does premium fuel cost vs regular on a road trip?
Premium typically runs 60 to 90 cents more per gallon than regular. On a 1,200 mile trip burning 43 gallons, premium adds $26 to $39 over regular. Use premium only if your owner’s manual lists it as “required.” If the manual says “premium recommended,” regular is acceptable and costs less per mile, with maybe 2 to 5 percent power and mpg reduction. If the manual says “regular,” premium is wasted money — the ECU cannot extract additional energy from higher octane.
Does running AC really hurt fuel economy that much?
Modern AC systems cost 1 to 4 mpg, depending on outside temperature and how hard the compressor is working. On a 90-degree-plus day, expect closer to the 4 mpg penalty. Driving with windows open at highway speed costs about 1 to 2 mpg due to aerodynamic drag. Above about 45 mph, AC is more efficient than open windows. Below 45 mph, open windows win. The old “windows down saves gas” rule only applies at city speeds.
How can I get the best fuel economy on a road trip?
Cruise at the speed limit or slightly below. Use cruise control. Keep tires at the door-jamb cold pressure spec. Skip roof cargo if possible — pack in the cabin instead. Don’t carry unnecessary weight. Use AC on hot days at highway speed (it beats open windows). Avoid heavy throttle inputs at on-ramps. These small habits stacked together can add 15 to 25 percent to your road trip mpg compared to aggressive driving with a loaded roof box.
Why We Built This
Most online trip calculators are sponsored by fuel apps or built into navigation tools and quietly assume your vehicle hits its EPA highway rating, which it almost never does in real driving. This one takes whatever mpg you actually get and tells you what your trip will cost based on the real number, plus lets you compare scenarios (slower vs faster, with vs without cargo) to see the financial trade-off before you leave. You can be the mechanic, and you can also be your own trip planner.
Help Us Make This Tool Better
Want EV per-mile cost added, or a way to model multiple stops with different fuel prices? Send us a note and we will look at every message. Tools improve when the people using them tell us what is missing.