How to Estimate Cost of Gas for a Road Trip

Couple road tripping at sunset
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Many people assume a road trip is a cheaper way to travel across the United States than flying, but that isn't always the case. It depends on the current gas prices and your car's mileage, so you should always calculate the cost of your potential road trip before you forego that plane ticket. To do this, you'll need to know the current price of gasoline, the miles per gallon your vehicle gets on the highway, and the miles you intend to drive on your trip. It's pretty simple, and you can get the bottom line in four easy steps.

Budgeting for a road trip

Calculate Your Gas Mileage

You first need to look up or calculate the mileage, or miles per gallon (mpg), your vehicle gets. You can do this yourself with simple math, or you can use an online mileage calculator. However, your actual mpg may vary depending on your particular driving style, for example, if you prefer to use cruise control or not. You can also try to figure it out by writing down the reading on your odometer the next time you fill up your car. If you have a computerized console, you could also set your trip odometer to zero by pushing the little knob underneath the odometer.

After setting the trip odometer or writing down the number, drive normally until it's time to fill up again, and note the odometer reading or the miles on the trip odometer when you fill it up again. Subtract the first odometer reading from the second to give you the number of miles you've driven. Or, if you set the trip odometer to zero when you filled up the last time, that figure is the number of miles you have driven on that tank of gas. Divide that number of miles by the number of gallons you just purchased on your second gas station visit, which will give you your miles per gallon.

Remember that your mileage will vary based on whether you spend more time driving on the highway or in town. City driving means you'll spend a lot of time stopping and starting, which uses more gas, so your mileage will be lower. If you use a whole gallon of gas to drive just on the highway, however, your calculation will be more accurate

Research Your Trip Distance

Next, calculate the total distance you'll be driving on your road trip. For this, you can use AAA or Google Maps. Enter in your starting and finishing points, along with any stops along the way, and then note the number of miles it says your trip will cover. Make sure you check that the route it's plotting out is likely to be the one you'll take.

If you're planning a several day-, week-, or month-long road trip, you might make some side trips or detours, so it would be impossible to calculate the exact distance. However, you can still make an educated guess by adding in some side trips to your total, so if you decide to skip out on them, you'll be spending less money than you budgeted for. Jot down the total distance you'll be driving, plus extra for potential side trips, next to your figure for miles per gallon.

Find Out the Current Price of Gas

For the third step, you need to know the current gas price to keep your total figure as accurate as possible. It's not possible to know the exact cost of a gallon of gas at any given time in any given location, but knowing the current price will provide you with a dependable approximation of the total fuel cost for your trip. Use AAA to find the average national gas price. Jot down the amount given at the top of the page as your third figure.

Add up Your Trip Cost

Take the mileage of the total distance of your trip and divide it by your miles per gallon to get the number of gallons of gas you will need on your journey. Then multiply that figure by the current gas price, and the result is the estimated cost of gas for your road trip.

For example, say you drove 200 miles after filling your car up, set your trip odometer to zero, and had to return to fill up again. On your return to the gas station, you topped up your tank with 10 gallons of gas. Your mpg would then be 200 divided by 10, which is 20 mpg. You are planning on driving 850 miles on your road trip, and the average price of gas was $2.34 at the time you checked.

To calculate the amount of money you need to budget for your road trip, divide 850 by 20 to get the number of gallons of gas you will need, which is 42.5. Multiply 42.5 by $2.34, which gives you $99.45 as the total cost of gas for your road trip. 

Don't Forget Other Travel Costs

The cost of gas is only one aspect of the expense of a road trip. You'll also need to factor in lodging, meals, maps, road tolls, and other car-related costs. If you're traveling with friends, you can divvy up the cost of gas, so your transportation fee will be even less per person.