How do you figure out your gas mileage for your vehicle?

How do you figure out your gas mileage for your vehicle?
First, you find out how many gallons your car can hold. then you fill it up and clock your mileage and watch your gas guage. when your tank is about 1/4 or 1/2 full or something, you divide your tank's capacity by 1/4 or 1/2 and divide your mileage by how many gallons you used and that number is the number of miles per gallon for your car. the way you drive also affects your gas mileage

Another way,

After you fill-up your tank, divide the miles you drove on that tank by the gals. of gas you just put in your tank. Example, I drove 300 miles and used 15 gals. of gas ( 300 divided by 15= 20 MPG ) hint, do this on 3 or 4 tanks in a row for a better avg.

Another Answer

The first way presented above is not too accurate, because not all fuel tank sending units are true to the gauge marks. Some cars have more mileage on the top half of the gauge while some have more mileage on the bottom. Accurate knowledge of how much fuel is being added to the equation makes the results more accurate.

1) Top off your tank and make note of the mileage
2) At your next fill-up, Top off again
3) Write down the number of gallons
4) Write down the mileage
5) Subtract the first mileage from the second to calculate the number of miles
6) Divide the number of miles by the number of gallons to calculate your gas mileage
7) Repeat this a few times (or continuously) to get your average gas mileage

The reason to use the "Top Off" method is because it is a more accurate way to repeatedly determine the number of gallons being added to the equation.