What is the most accurate way to determine gas mileage in my car?

Question

I know my fuel tank holds 17.2 gallons. I fill my car up....then figure my gas mileage based on how much gas I purchased.

example:

My last fill up I purchased 10.772 gallons of gas. So I drove 318.9 miles on that 10.772 gallons of gas.

318.9 / 10.772 = 29.60 MPG

Is this the most accurate way of doing things? Or am I assuming wrong that my gas tank holds exactly 17.2 gallons of gas (which is what the manual says it holds)

Answer 1

MPG is based on fuel consumption and has nothing to do with the tank size. You used the proper equation to find your MPG. You have obtained the "overall" fuel mileage. You can do the same with driving strictly on freeways for at least 100 miles, at steady speeds, to find your highway milage.

Answer 2

You should go to the gas station nearest your home and fill the tank. Then go out and drive atleast 100 miles before filling up again. When you do fill up, go back to the same gas station and the SAME PUMP as well. Fill the car up again and write down how many gallons went in.  ( make sure to let the pump auto-stop when filling up! do not top it off)

Once you have that figure you can check your odometer, and then do your formula. It's best to do this a few times to get a real average number.

Answer 3

Fill your tank, don't fill it again after the pump stops. Reset your trip computer, drive until half your tank or more is gone,  fill up the same way as before. Then Trip Computer/Gallons of gas you just put in.

Answer 4

That is the best way to calculate actual mileage.  Even though your gas tank technically holds 17.2 gallons, due to the shape and configuration of the tank, you may only have 15 or 16 gallons of useable volume.