Do you multiply or divide to change gal to fl oz?

To convert gallons to fluid ounces, you multiply. There are 128 fluid ounces in one gallon, so you multiply the number of gallons by 128 to get the equivalent amount in fluid ounces. For example, if you have 2 gallons, you would calculate 2 x 128 to find that it equals 256 fluid ounces.