A fluid ounce (US) is a unit of volume equal to about 29.6 ml, 1/16 pint, 1/8 cup, 2 tablespoons, and 6 teaspoons. A fluid ounce is different than an ounce. A fluid ounce measures volume, whereas an ounce measures mass. In other words, a fluid ounce measures how big something is, and an ounce measures how heavy something will feel.
Notably, one fluid ounce is equal to 1/16 pint, and one ounce is equal to 1/16 pound. Also, one pint of water (or beer) at room temperature has approximately one pound of mass (“a pint’s a pound, the world around”). So, one fluid ounce of water is about equal to one ounce. However, one fluid ounce of other substances may not necessarily weigh the same.