How to Calculate Fuel Cost for a Road Trip

Knowing how to calculate fuel cost for a road trip is one of the most practical skills any driver can have. Whether you are planning a weekend getaway, a cross-country adventure, or just need to split gas money with friends, an accurate fuel estimate keeps your budget on track and eliminates unpleasant surprises at the pump.

The good news is that the math behind fuel cost estimation is straightforward. In this guide, we will walk through the core formula step by step, show you a worked example with real numbers, and share tips from seasoned road trippers on Reddit communities like r/roadtrip and r/frugal for keeping your gas budget as low as possible.

The Core Fuel Cost Formula

Every road trip fuel estimate starts with the same equation. As Calculator.net and SoFi's gas cost guide both explain, the formula is:

Breaking this down: Distance ÷ MPG tells you how many gallons you will need. Multiply that by the price per gallon, and you have your total fuel cost. That is all there is to it—three numbers in, one answer out.

Step-by-Step Worked Example

Let us put the formula into action with a realistic scenario. Suppose you are driving from Dallas, Texas to New Orleans, Louisiana—roughly 450 miles one way. Your car gets 30 MPG on the highway, and the average gas price along your route is $3.50 per gallon.

Step 1: Estimate Your Distance

Use Google Maps, Apple Maps, or Waze to find the driving distance. Search your starting point and destination, and note the total mileage. Google Maps will typically show multiple routes—pick the one you plan to take. For our example, Dallas to New Orleans is approximately 450 miles via I-20 and I-49.

Step 2: Determine Your Car's MPG

You can find your vehicle's fuel economy in two ways. The most accurate method is to calculate it manually using the tank-to-tank method: fill up, drive, fill up again, then divide miles driven by gallons used. Alternatively, look up your car's EPA estimate at FuelEconomy.gov—just keep in mind that real-world MPG is often 3–5 MPG lower than the EPA highway number, especially in mixed driving conditions.

Step 3: Find the Current Gas Price

Check GasBuddy's Trip Cost Calculator for current prices along your route. Gas prices vary significantly by state—as of early 2026, the national average hovers around $3.30–$3.60 per gallon, but states like California and Washington often exceed $4.50, while Texas and Mississippi tend to stay under $3.00.

Step 4: Run the Calculation

So this one-way trip will cost approximately $52.50 in gas. For the round trip, simply double it: $105.00. As Reader's Digest points out, always remember to account for both legs of the journey when budgeting—it is a common oversight that can throw off your entire travel budget. For a deeper look at costs for longer trips, see our guide on how much it costs to drive 1,000 miles.

Gas prices can vary by more than $1.50 per gallon between states, making route planning a real money-saver.

Calculating Your Cost Per Mile

Another useful number to know is your cost per mile, which helps you quickly estimate the fuel cost of any trip without pulling out a calculator each time:

Once you know your cost per mile, estimating any trip is instant. A 200-mile day trip? That is 200 × $0.117 = $23.40. A 1,500-mile cross-country drive? Roughly $175. This is the same approach that ride-share drivers and trucking companies use to track fuel expenses.

Round Trip vs. One-Way: Budget Smart

If you are driving to a destination and back, doubling the one-way cost gets you close—but not always exact. Here is why:

• Gas prices differ by location. You might fill up cheaply in Texas on the way out but pay $0.50 more per gallon in Louisiana on the return. Use GasBuddy to plan which stations to hit on each leg.
• Driving conditions change. The return trip might involve more city driving, different traffic patterns, or elevation changes that affect your MPG. Hilly or mountainous terrain can reduce fuel economy by 10–20%.
• Detours add up. Side trips to attractions, restaurants, or scenic routes add miles. Experienced road trippers on r/roadtrip commonly recommend budgeting 10–15% extra on top of your calculated fuel cost to cover detours and unexpected reroutes.

How to Find Your Car's Real MPG

The accuracy of your fuel cost estimate depends entirely on using a realistic MPG number. Here are three ways to find yours:

• Manual calculation (most accurate): Fill your tank, reset the trip odometer, drive normally until the next fill-up, then divide miles driven by gallons used. Our MPG calculator walks you through this process.
• EPA estimates (quick reference): Visit FuelEconomy.gov and enter your vehicle's year, make, and model. Keep in mind that EPA highway numbers are tested in lab conditions—real-world highway MPG is typically 5–10% lower, and city MPG can be 15–20% lower.
• Dashboard display (least accurate): Your car's onboard computer shows an MPG estimate, but studies have found these readings are often 5–15% optimistic. Use it as a ballpark, not a budget number.

For road trip planning specifically, use your highway MPG if the trip is mostly interstate driving, or use the combined MPG if you will be mixing highway and city streets. When in doubt, round down—it is better to overestimate fuel costs than to run short.

Current Gas Prices and How They Vary

Gas prices are the most unpredictable variable in the fuel cost equation. According to GasBuddy, prices can differ by more than $1.50 per gallon between the cheapest and most expensive states. Here is a snapshot of how prices typically stack up:

For the most accurate estimate, check GasBuddy or FuelEconomy.gov's Trip Calculator the day before your trip. Prices update daily, and even a $0.30 per gallon difference can add $5–$10 to a long road trip.

Tips for Reducing Your Road Trip Fuel Cost

Once you know the basic math, here are practical ways to bring that number down—pulled from expert guides and real driver advice on Reddit:

• Use GasBuddy to find the cheapest stations along your route. The GasBuddy Trip Cost Calculator maps out gas stations and their current prices between any two points. Drivers on r/frugal regularly report saving $10–$20 on long trips just by choosing cheaper stations.
• Drive at moderate speeds. Fuel economy drops significantly above 55 MPH. Driving at 65 instead of 75 on the highway can improve your MPG by 10–15%, potentially saving $15–$25 on a 1,000-mile trip.
• Check tire pressure before departure. Underinflated tires increase rolling resistance and reduce MPG by up to 3%. A quick pressure check at the gas station before you leave costs nothing but can save a few dollars in fuel.
• Avoid excessive idling. Sitting in drive-throughs, waiting with the engine running at rest stops, and idling in traffic all burn fuel without moving you forward. Turn off the engine if you will be stopped for more than 30 seconds.
• Pack light. Every extra 100 pounds reduces fuel economy by about 1–2%. Roof cargo carriers are especially costly—they can reduce MPG by up to 25% at highway speeds due to aerodynamic drag.
• Fill up at warehouse clubs. Costco, Sam's Club, and BJ's typically price gas $0.15–$0.30 below nearby stations. If one is near your route, it is worth the stop.
• Be smart about AC. Air conditioning can reduce your fuel economy by 5–25%, especially in city driving. Learn exactly how much in our guide: does air conditioning use more gas?

Quick Note for International Travelers

If you are visiting the US from a country that uses kilometers and liters, or if you are an American renting a car abroad, here are the key conversions:

• 1 mile = 1.609 kilometers
• 1 US gallon = 3.785 liters
• To convert MPG to L/100km: divide 235.215 by the MPG number (e.g., 30 MPG = 7.84 L/100km)
• To convert km to miles: multiply kilometers by 0.621

For metric countries, the fuel cost formula becomes: Fuel Cost = (Distance in km ÷ km per liter) × Price Per Liter. The logic is identical—only the units change.

Online Tools That Do the Math for You

If you prefer a hands-off approach, several reliable online tools can estimate your road trip fuel cost automatically:

• FuelEconomy.gov Trip Calculator — Official US government tool. Enter your car and route to get a fuel cost estimate based on EPA data and current gas prices.
• GasBuddy Trip Cost Calculator — Uses crowd-sourced, real-time gas prices along your specific route. Great for finding the cheapest fill-up stops.
• Calculator.net Fuel Cost Calculator — Simple and clean interface for quick one-off calculations.
• Our Fuel Cost Calculator — Built for quick estimates with support for both US and metric units.

Frequently Asked Questions