Estimate road trip fuel cost (and stops)

Last Updated: February 12, 2026

Why Your Mental Math on Fuel Costs Is Usually Wrong

A 1,520-mile round trip from Denver to Vegas in a 24 MPG SUV turns into real fuel money fast. Your true highway MPG, the return leg, and a detour buffer move the road trip fuel cost more than the number on the pump sign suggests. The per-leg view below is where it gets honest.

This planner calculates fuel consumption for your actual route, with your vehicle's MPG and current gas prices. The result tells you what to budget before you leave, not what to scramble for when the tank hits empty in the middle of Nevada. Plug in your numbers, add a buffer for detours and traffic, and lock in the real fuel cost.

What Your Fuel Estimate Includes

Fuel Math in Plain English

The formula is simple: Distance ÷ MPG = Gallons. Then Gallons × Price = Cost. A 500-mile trip in a car that gets 25 MPG needs 20 gallons. At $3.50/gallon, that's $70. Round trip doubles it to $140.

Where people mess up: using the EPA sticker MPG instead of real-world highway MPG (usually 10-15% lower), forgetting return trips, and not accounting for city driving at each destination. If you'll be sitting in LA traffic for two hours, your 28 MPG highway car is getting 18 MPG during that stretch.

The buffer percentage matters. A 10% buffer on a 1,000-mile trip adds 100 miles worth of fuel, about $15-20 extra. That covers detours, getting lost, side trips to that diner you saw on the highway, and the gas station you passed hoping for a cheaper one ahead.

Sample Trip: Denver to Vegas and Back

A long weekend from Denver to Las Vegas, three people splitting the gas, one SUV at a real-world 24 MPG. Break it into legs and add a buffer before trusting the total.

Result: round it to $82 a head and budget $250 for fuel, leaving a small cushion for price spikes in rural Nevada. The buffer line is what separates that figure from the optimistic "probably $150" guess the trip started with.

Round-Trip vs One-Way Planning

One-way trip: Enter the distance once. You're relocating, someone else is driving back, or you're flying home. Straightforward math.

Round-trip: Either double your distance entry or add two legs (outbound and return). The return leg might be different if you're taking a scenic route back or stopping somewhere new.

Multi-stop trips: Break it into legs. Denver to Moab (350 miles), Moab to Vegas (460 miles), Vegas to Denver (750 miles). Each leg gets its own calculation, and you can see where the fuel dollars go. Most people discover that the "quick detour" they added costs more than expected.

MPG Reality Checks

Your EPA sticker lies. That number comes from lab tests. Real-world highway MPG runs 10-15% lower. If your sticker says 30 MPG highway, plan for 26-27 MPG.

Speed kills efficiency. Going 80 mph instead of 65 mph can drop your MPG by 10-15%. Wind resistance increases with the square of speed. That extra 15 mph might cost you $30-50 on a long trip.

Load matters. A roof rack (even empty) drops MPG by 2-5%. Loaded roof box? 10-25% hit. Towing a trailer? Expect 25-40% worse fuel economy. If you're pulling a camper, your 22 MPG truck becomes a 14 MPG truck.

AC in summer, heat in winter. Both affect MPG, but AC hits harder, 3-5% in most vehicles. Not enough to skip it in Arizona, but enough to factor in.

Building the Trip Leg by Leg

Step 1: Add trip legs. Name them ("Denver to Moab") and enter the distance. Use Google Maps for accurate mileage. Don't guess.

Step 2: Enter your vehicle's real-world MPG. Check your last few fill-ups if you track it, or knock 10-15% off the EPA highway number.

Step 3: Enter current gas price per gallon. Check GasBuddy for prices along your route. They can vary by $0.50+ between states.

Step 4: Add a buffer (10-15%) for detours, traffic, and the inevitable "let's check out that overlook."

Step 5: If splitting costs, enter the number of people. The per-person breakdown shows up automatically.

Edge Cases That Blow Up the Estimate

• Mountain driving: Climbing from Denver (5,280 ft) to Eisenhower Tunnel (11,158 ft) tanks your MPG by 20-30%. The descent recovers some, but net effect is worse fuel economy on mountain routes.
• Towing or heavy load: Pulling a trailer or loaded to the roof? Cut your MPG estimate by 25-40%. That 28 MPG car becomes an 18 MPG truck.
• Price jumps between states: California gas runs $1-2 higher than Nevada. Plan fill-ups before state lines when crossing into expensive territory.
• Heavy headwinds: Driving west into prevailing winds can drop MPG by 5-10%. Check weather forecasts for wind direction on long stretches.
• City driving at destinations: Two days of city driving in LA burns more gas than you'd expect. Add 30-50 miles of city equivalent per day if you're doing lots of local driving.

Fuel Stop Strategy for Long Drives

Don't wait until empty. Fill up when you hit 1/4 tank in remote areas. Gas stations can be 80+ miles apart in Nevada, Utah, and Wyoming. Running out between towns is expensive (tow truck) and dangerous.

Price scout before state lines. Gas in Utah is often $0.30-0.50 cheaper than Nevada. Fill up in St. George before crossing into Nevada. Same logic applies at every state border. Check GasBuddy.

Off-highway is usually cheaper. Gas stations right off the interstate charge $0.20-0.40 more. Drive 2 miles into town for better prices. Worth it on a 70-gallon trip.

Time your stops. Combine gas with bathroom breaks and food. Four 15-minute stops beat eight 8-minute stops for total trip efficiency and driver alertness.

Fuel and mileage questions

How do I find my car's real MPG?

Fill up completely, reset your trip odometer, drive normally until you need gas again, fill up again, then divide miles driven by gallons added. Do this 3-4 times and average the results. Your real MPG is usually 10-15% below the EPA sticker.

Should I use regular or premium gas?

Use what your owner's manual says. If it says "regular recommended," premium won't help. If it says "premium required," using regular can damage the engine over time. Don't pay extra for no benefit.

Is it cheaper to fly or drive?

Break-even is usually around 500-700 miles for a solo driver. Add passengers and driving wins fast. 4 people splitting gas beats 4 plane tickets almost every time. But factor in lodging for multi-day drives.

How much should I budget for a cross-country drive?

NYC to LA (2,800 miles) in a 25 MPG car at $3.50/gallon = about $400 in fuel one way. Round trip is $800. Add 10-15% buffer for detours and price variation.

Does driving slower really save gas?

Yes. Most vehicles hit peak efficiency around 45-55 mph. Going 75 instead of 65 can cost 10-15% more fuel. On a 1,000-mile trip at $3.50/gallon in a 25 MPG car, that's $15-20 extra.

Related Trip Planning Tools

• Flight Carbon Emissions Estimator. Compare your road trip's footprint to flying
• Hotel vs Airbnb Cost Comparison. Budget lodging for overnight stops
• Vacation Travel Budget. Plan total trip costs beyond just fuel
• Commute Cost Calculator. Same math, daily scale for regular drives

Sources

• FuelEconomy.gov. EPA fuel economy ratings and real-world driving tips
• AAA Gas Prices. State-by-state average prices updated daily
• U.S. Energy Information Administration. National fuel price data and trends