There are 128 ounces in a gallon. This measurement is particularly useful when you are tracking how much water you have drank that day. In order to try and find out how many ounces there are in a gallon by yourself, all you have to do is multiply the number of gallons by the number of ounces. So if you have 2 gallons and you want to figure out how many ounces are in 2 gallons, all you need to do is multiply 2, the number of gallons, by 128, the number of ounces in a gallon.
So 2 times 128 is 256 ounces. Other types of helpful things to know are that there are 8 ounces in a cup, 2 pints in a quart, 2 cups in a pint, and 4 quarts in a gallon. There are many times where you will need to know this information.
