Everyday · 4 min read
How to Estimate Fuel Cost for a Road Trip
Before you leave for a road trip, it helps to know roughly what you will spend on gas. Our fuel cost calculator gives you an instant number, but the math behind it is simple enough to do in your head with a rough estimate, or on paper for a more precise one.
The basic formula
Fuel cost comes down to three numbers: the distance you plan to drive, your vehicle's fuel efficiency in miles per gallon, and the price of fuel where you will be buying it. Divide the distance by the MPG to get gallons needed, then multiply by the price per gallon. A 400 mile trip in a car that gets 25 MPG needs 16 gallons. At $3.50 a gallon, that is $56.
Why your real MPG differs from the sticker number
The MPG figure on a car's window sticker is an average from controlled testing, not a guarantee. Highway driving at a steady speed usually gets closer to that number than city driving with frequent stops. Higher speeds increase wind resistance, which lowers MPG on the highway too, so cruising at 80 mph instead of 65 mph can cost noticeably more in fuel over a long trip. Mountainous terrain, a loaded trunk, and running the air conditioning all reduce efficiency as well.
Estimating cost for an unfamiliar route
If you do not know your car's exact MPG, check the owner's manual or look at your last few fill ups: divide the miles driven since the last fill by the gallons it took to fill the tank again. For fuel prices, use the price at your departure point as a baseline, but expect some variation along the route, since prices can differ by 20 to 30 cents a gallon between regions and even between neighboring towns.
Splitting the cost between passengers
For a shared trip, divide the total fuel cost by the number of people splitting it. A $120 fuel bill split four ways is $30 per person. This is usually a fairer way to divide road trip costs than splitting all expenses evenly regardless of who drove or how many people rode in each car, especially if the group is taking two vehicles with different fuel efficiency.
Accounting for a round trip
Remember to double the one-way distance if you are estimating for the full trip there and back, and add any detours or side trips you plan to take once you arrive. A 300 mile drive to a destination with 50 miles of local driving once you get there and the same 300 miles home totals 650 miles, not 300.
Comparing gas and electric costs
If you are deciding between a gas vehicle and an EV for the trip, the comparison is straightforward: gas cost is distance divided by MPG times price per gallon, while electric cost is distance divided by miles per kWh times the price per kWh. Electric rates are usually lower per mile, but charging time and station availability matter more on longer routes than they do for daily driving.
Other trip costs to budget for
Fuel is usually the largest single expense on a road trip, but not the only one. Tolls, parking, and any wear-related maintenance like an oil change before a long drive add to the real cost of the trip. A rough total budget should include a buffer for at least one unplanned stop, since running the numbers on fuel alone can make a trip look cheaper than it ends up being once tolls and food are added in.
Frequently asked questions
How do I calculate how much gas a road trip will cost?
Divide the total distance by your car's miles per gallon to get gallons needed, then multiply by the price per gallon. A 400 mile trip at 25 MPG and $3.50 a gallon costs about $56.
Does driving speed affect fuel cost?
Yes. Wind resistance increases with speed, so driving faster on the highway lowers your MPG and raises fuel cost per mile, even though you get there sooner.
How do I split fuel cost between passengers?
Divide the total fuel cost by the number of people sharing the trip. Four people splitting a $120 fuel bill each pay $30.