How to Calculate Miles Per Gallon

Calculating MPG

In this time of fluctuating gas prices, learning how to calculate miles per gallon can help you budget your gas expenses for the month. When you combine your miles per gallon with the average amount of driving you do in a week or month, you’ll have a pretty good idea how much money you spend on gas. Calculating miles per gallon isn’t that hard. More than anything, you just need to get in the habit of writing down your mileage every time you fill up your gas tank. Then mastering how to calculate your miles per gallon simply becomes a matter of basic math.

With that in mind, here’s an easy 6-step process for how you calculate miles per gallon, as well as suggestions for testing the accuracy of your gas mileage calculations.

Buy A Handheld Notepad – Buy a small notepad that will fit in your glove compartment. Keep this note pad along with a pen or pencil handy to keep notes on your miles per gallon ratio.
Note When Fill Up Your Gas Tank – The next time you fill up your gas tank, take out your notepad and write down the mileage on your speed-o-meter.
Take Notes On Your Next Refill – Drive as you normally would, until your next fill-up. Once you drive up to the gas tank, take out your notepad and write down the mileage on your speed-o-meter again.
Record Gallons of Gas You Pump – Also, record the number of gallons you pumped into your car on your second refill. This number will be important in your calculations.
Do The Math – Once you get home, use your notepad for some basic math. Subtract the mileage from your first fill-up from the mileage on your second fill-up. Put another way, subtract the number you recorded in Step 2 from the number you recorded in Step 3. For instance, let’s assume you had 55,200 miles on your first fill-up and 55,500 miles on your second fill-up. You will have drive 300 miles between refills of your tank.
Divide Miles Driven by Gallons Pumped – Now, divide the number of miles you drove between refills by the number of gallons you pumped into your car on the second refill. If that’s confusing, divide the number you got in Step 5 by the number you recorded in Step 4. So if you pumped 15 gallons into your car on your second refill and you drove 300 miles between refills, then you would divide 300 by 15. The result would be 20. Therefore, you are getting 20 miles per gallon from your vehicle.

Repeat To Assure Gas Mileage Accuracy – If you want greater accuracy or want to assure yourself that your calculations were right, you might get into the habit of taking down your mileage between trips to the pump and gallons pumped at each refill. Do the math each time and compare your calculations. Remember that your gas mileage in town will be less than gas mileage on the highway, because acceleration from stopping and starting at lights requires more gas, and because you burn gas idling at lights. This might account for fluctuations in your gas mileage, and is a good reason not to take any one calculation as the absolute gauge of how much mileage you get per gallon.

How To Calculate Gas Budget for a Month

Calculate Miles Driven Per Month – Once you have your gas mileage figured, keep track of how many miles you drive per month. You’ll need to record the miles on your car on the first day of one month, then record the miles on your car the first day of the next month. Subtract the miles recorded on the first month from the miles recorded on the second month. This will tell you how many miles you drive per month.
Divide Miles Driven Per Month by Your Miles Per Gallon – Divide the number you get under miles driven per month (A) by miles you get per gallon (6). This will give you the gallons of gas you consumed in that month.
Multiply Gallons Consumed Per Month by Current Gas Prices – When you fill up your gas tank, write down the price per gallon of the gas you buy. If the prices have fluctuated throughout the month, you might calculate an average gas price for the month. If the gas prices haven’t fluctuated much, simply take gas prices and use that in your multiplication. Multiply the number of gallons you consume in a month (B) by the current gas prices. This will give you the amount of money you spent on gas for the month.

Once you have this figure, you’ll be able to guess within a reasonable amount how much money you spend per month on gas. Do these same calculations several months in a row to get an average, because there might be a deviation from one month to the next. After several months, you’ll have a pretty good idea what your average gas consumption and your average gas budget is. You can then place that figure into your monthly household budget.

Obviously, gas prices will fluctuate greatly, due to the season of the year (gas goes up in summer, when people are on vacation and consuming more gas) and other market factors. So the most important number to calculate is your miles per gallon, because this is the one factor that is under your control. Once you have an idea of your standard gas consumption per month, all you have to do is multiply that number by the current price of gas to recalculate your gas budget.