Gas Trip Cost Calculator
Plug in your distance, your vehicle's fuel efficiency, and the price of gas to estimate what a road trip will actually cost, then split it fairly across everyone riding along.
Last updated
Defaulted to a reasonable national average, edit it to match your local price.
How to estimate road trip gas costs
The math behind a road trip gas estimate is simple once you have the three key numbers: how far you're driving, how efficiently your vehicle uses fuel, and what gas costs where you'll be buying it. In miles and gallons mode, the calculator divides your total distance by your vehicle's MPG to get the gallons you'll burn, then multiplies that by the price per gallon to get your total cost. For kilometers and liters, the formula flips slightly: it divides distance by 100, multiplies by your car's liters-per-100km rating to get liters needed, then multiplies by the price per liter. Round trips simply double the one-way distance before any of that math runs.
Here's a worked example using the calculator's own placeholder numbers: a 450 mile one-way trip in a car that gets 28 MPG, with gas at $3.50 a gallon. Fuel needed is 450 divided by 28, which comes out to 16.1 gallons, and multiplying that by $3.50 gives a total cost of $56.25. Split three ways between passengers, that's $18.75 each. Make it a round trip and the distance doubles to 900 miles, pushing fuel to 32.1 gallons and total cost to $112.50. In metric units, a 500 km trip in a vehicle rated at 8 L/100km with gas at $1.50 a liter needs 40 liters (500 divided by 100, times 8) for a total of exactly $60.00.
MPG and fuel-cost math here follows standard EPA fuel economy reporting conventions, check fueleconomy.gov for your specific vehicle's rating.
The biggest source of error in any gas cost estimate is the MPG number itself. EPA window-sticker ratings are measured under controlled conditions, and real-world highway driving can come in noticeably above or below that figure depending on speed, headwinds, air conditioning use, and how loaded down the vehicle is with luggage or passengers. None of this accounts for tolls, food, or lodging either, it's purely the fuel. Still, fuel is usually the single biggest variable cost on a road trip, so getting a solid number upfront, even a slightly imperfect one, makes budgeting the rest of the trip much easier.
Tips to save on gas for long trips
- Use cruise control on the highway, it smooths out acceleration and can meaningfully improve fuel economy.
- Check your tire pressure before you leave, underinflated tires increase rolling resistance and burn more gas.
- Plan your route to avoid unnecessary detours and heavy traffic corridors when a similar-length alternate exists.
- Clear out excess weight from the trunk, extra cargo makes your engine work harder over long distances.
- Use a gas price app to find the cheapest stations along your route instead of filling up wherever is convenient.
- Avoid unnecessary idling at rest stops, and pack your own snacks and drinks to cut down on extra stops.
Frequently asked questions
How accurate is this estimate?
It's a solid ballpark based on distance, your vehicle's average fuel efficiency, and the gas price you enter. Real trips vary with driving style, load, and road conditions, so treat the number as a planning estimate rather than an exact total.
Does this account for traffic or elevation?
No. Traffic, hills, and highway versus city driving all affect real-world fuel economy, sometimes significantly. If your route has a lot of mountains or stop-and-go traffic, consider lowering your MPG input a bit to get a more realistic estimate.
How do I find my car's MPG?
Check your owner's manual or the window sticker for the EPA-estimated combined MPG, or look up your exact make, model, and year on fueleconomy.gov. You can also calculate your own average by dividing miles driven by gallons used over a few fill-ups.
Should I use city, highway, or combined MPG for a road trip?
Highway MPG is usually the better input for a road trip estimate, since most cars get better mileage at steady highway speeds than they do in city stop-and-go driving. Combined MPG blends city and highway together, so it can slightly underestimate how far a gallon goes on a mostly-highway route, while city MPG would overestimate your gas cost.
Why does switching to kilometers ask for L/100km instead of km per liter?
L/100km is the standard metric fuel economy convention because it plugs directly into the cost formula: divide your distance by 100 and multiply by the L/100km rating to get liters needed. Km per liter behaves the opposite way, a bigger number means better efficiency, which makes it awkward for calculating fuel needed rather than just comparing vehicles.
How do I estimate a trip with multiple stops or a multi-leg route?
Add up the one-way distance for every leg of your route using a mapping app, then enter that combined total as your one-way distance here with round trip set to no, since you've already accounted for the full path. Treating a multi-stop trip as one total distance keeps the math accurate even though your actual drive isn't a straight line.
If gas prices go up 10%, does my total cost also go up 10%?
Yes, exactly. Total cost is fuel needed multiplied by price per gallon or liter, and fuel needed doesn't change when the price does, so the relationship between price and total cost is perfectly linear. A 10% price increase means a 10% higher total, regardless of your distance or MPG.