The U.S. fluid ounce is (1/128) gallon, about 1.805 cubic inches or 29.573531 ml. This volume of water weighs about 1.04 ounces.
The Imperial fluid ounce is (1/160) gallon or 8 fluid drams, about 1.734 cubic inches or 28.413063 ml. This volume of water weighs exactly 1 ounce under certain temperature and pressure conditions.
