How Much is a Fluid Ounce?

A fluid ounce is a measure of volume. The ounce is a measure of weight. This is very confusing and has lead to many mishaps. The fluid ounce in metric terms is stated as 29.573531 milliliters. It is called an ‘ounce’ because at one time in antiquity, a fluid ounce of water weighed one ounce (probably using British weight measures).