A fluid ounce (abbreviated fl oz, fl. oz. or oz. fl., old forms ℥, fl ℥, f℥, ƒ ℥) is a unit of volume (also called capacity) typically used for measuring liquids. Various definitions have been used throughout history, but only two are still in common use: the British Imperial and the United States customary fluid ounce. An imperial fluid ounce is 1⁄20 of an imperial pint, 1⁄160 of an imperial gallon or approximately 28.4 ml. A US fluid ounce is 1⁄16 of a US fluid pint and 1⁄128 of a US liquid gallon or approximately 29.57 ml, making it about 4% larger than the imperial fluid ounce.
US customary fluid ounce
| 1 US fluid ounce | = | 1⁄128 | US gallon |
| | = | 1⁄32 | US quart |
| | = | 1⁄16 | US pint |
| | = | 1⁄8 | US cup |
| | = | 1⁄4 | US gill |
| | = | 2 | US tablespoons |
| | = | 6 | US teaspoons |
| | = | 8 | US fluid drams |
| | = | 1.8046875 | cubic inches |
| | = | 29.5735295625 | millilitres |
| | ≈ | 1.040842731 | imperial fluid ounces |