A single ounce of water weighs .0625 pounds, or approximately 28 grams. Since liquids are measured in ounces, the weight of an ounce of water is the same as an ounce of any other type of matter.
An ounce of water can also be broken down into other conversions. It weighs more than 28,000 milligrams. Interestingly, water becomes lighter when frozen. This means that an ounce of water weighs less when it is in a frozen state, which is why ice floats when placed in a glass of water. Ice takes up more space than water, which leads some to believe that it is heavier.