Your Four-Step Guide to Calculating Gas Mileage for a Road Trip

How to Make a Gas Mileage Calculator Work for Your Road Trip Budget

Couple road tripping at sunset
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You're thinking a U.S. road trip sounds like a cheap way to travel across the country. Is it? Let's take a look at the current gas prices in the United States and learn how to calculate the mileage for your particular trip. Don't worry if this sounds like a lot of hard work -- it isn't. Below you'll find four simple steps to help you to calculate how much your entire road trip will cost you in gas.

1. How to Calculate Gas Mileage (MPG): Find Out How Much It Costs You to Drive One Mile

First thing you want to do is calculate the miles per gallon (MPG) to help you figure out how much it'll cost you to drive one mile. The easiest way to do this is with a mileage calculator or by doing it yourself:

If you want to do it yourself, the next time you fill up your car, note your odometer reading or set your trip meter to zero (push in the little knob underneath the odometer or use your computerized console).

In addition, you'll want to make a note of the number of gallons you've just purchased, down to the tenth. You should now drive as normal until it's time to fill up again, then one more, note the odometer reading when you fill it up.

Your first step towards calculated your gas mileage is to subtract the first odometer reading from the second to give you the number of miles you've driven. If you reset your odometer to zero, this will just be the second odometer reading.


Then, you'll want to divide that figure by the number of gallons you just purchased on your second visit to the gas station, and this will give you your MPG. Write down this number as we'll be using it later on.

Related: Improve your gas mileage and fuel efficiency with a few simple tips.

2. Calculate Your Trip Distance

Next, you'll want to calculate the total distance you'll be driving.

For this, you can use this great little online trip distance calculator, AAA or simply Google Maps. Enter in your start and finish points, along with any stops along the way, check that the route it's plotting out is likely to be the one you'll be taking, and then make a note of the number it gives you.

If you'll be heading out a multi-day/week/month road trip then you obviously won't know the exact distance (due to side trips and random detours), so it's best to make a guess based on your planning so far. If in doubt, add 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 next to your figure for MPG.

Step 3: Find Out the Current Price of Gas

For the third step, you'll want to look up the current price of gas to keep your total figure as accurate as possible. I recommend using AAA to find the average national gas price. Jot down the amount given at the top of the page as your third figure.

Step 4: Calculate Your Trip Cost

It's time to calculate the total cost of your trip!

First, you'll want to take the number you wrote down in step 2 (the total distance of your trip) and divide it by the number you got from step 1 (your gas mileage).

Next, multiply that figure by the number you wrote down in step 3 (the current price of gas), and then you're all done! The figure you're left with is how much money you'll have to spend on gas during your road trip.

An Example to Help You Out

Let's say you went to the gas station and set your odometer to zero. Then, you drove 200 miles before you needed to refill your tank. 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. 

For step two, you would calculate how far you're going to be driving on your road trip: let's say you'll be doing 850 miles in total. 

For step three, you looked up the average price of gas and found it to be $2.34. 

To calculate the total amount of money you need to budget for your road trip, you want to divide 850 by 20 to get 42.50 and then multiply it by $2.34, which gives you $99.45 as the total cost of gas for your road trip.


Remember to Factor in All Car Travel Costs

The cost of gas alone is only a small part of your trip expense planning. Remember that you'll also need to factor in any lodging, meals, maps, entrance fees, and other car-related costs, like oil, too.

This article was edited by Lauren Juliff.