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Road Trip Gas Cost Calculator (MPG, Round Trip, Split)

Find the gas cost of a road trip from miles, MPG and gas price: round trip, cost per person, gallons, fill-ups and cost per mile.

Tool inputs stay in your browser · optional AI search sends your query

Good to know: Scope: the gasoline (or diesel) cost of one car trip in the U.S., using miles, miles per gallon (MPG) and price per gallon, with an optional round trip, cost split, tank size and a second car to compare. Not included: tolls, parking, food, lodging, rental fees, wear and tear, the IRS mileage rate (see the US Mileage Log tool for that), EV charging (see the EV Charging Cost Calculator) and price changes between gas stations along the way. The math is the EPA fuel cost formula used on window stickers: cost = fuel price ÷ MPG × miles. Use your car’s combined MPG from fueleconomy.gov, or its highway MPG for a trip that is mostly interstate. Default gas price: $4.27 a gallon (EIA U.S. average regular gasoline, week of October 26, 2026). Prices change and differ by state, so type the price you see at your local pump. Extra fuel: fueleconomy.gov says a roof cargo box can cut fuel economy by about 10% to 25% at interstate speeds (65 to 75 mph) and a rear-mount box by about 1% to 5% on the highway, and that each 5 mph over 50 mph is like paying about $0.21 more per gallon; add a percent if you will carry a roof box, a heavy load or drive fast. Fill-ups assume you start with a full tank and refill at about a quarter tank (a ToolsKo safety habit, not an official rule). Everything stays in this browser tab; nothing is sent or saved. Independent ToolsKo estimate. Sources reviewed November 12, 2026.

How to use it (step by step)

  1. 1Type the one-way distance in miles (your map app shows it) and pick round trip or one way.
  2. 2Type your car’s MPG (on the window sticker or fueleconomy.gov) and the gas price at your local pump. Add extra fuel % if you carry a roof box or heavy load.
  3. 3Read the total gas cost, the cost per person if friends are splitting it, and how many fill-ups to plan. Add the tank size or a second car’s MPG to see more.

Words to know

MPG (miles per gallon)
How many miles your car goes on one gallon of gas. Higher is better. The window sticker shows city, highway and combined MPG.
Combined MPG
One number that mixes city and highway driving. The EPA uses it for the yearly fuel cost on the sticker.
Round trip
There and back again, so the miles are doubled.
Cost per mile
What each mile of driving costs you in gas. Handy for splitting or paying someone back for a ride.

Explore tools for Australia, the US & Europe →

Sources & methods

References checked November 11, 2026. Read each tool’s scope and assumptions before relying on its result.

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