What is a Fluid Ounce?

The US fluid ounce equals exactly 29.5735295625 milliliters and is the standard small-volume unit for beverages, cocktails, personal-care products, and cooking in the United States. It is distinct from the (weight) ounce: 1 fluid ounce of water weighs about 1 ounce by weight at room temperature, but other liquids may weigh more or less. Soft-drink cans (12 fl oz), beer bottles (12 fl oz), shampoo bottles, and skin-cream tubs all label volume in fluid ounces. The US fluid ounce is slightly different from the UK imperial fluid ounce (28.4131 mL — about 4% smaller), reflecting the different gallon definitions. The US fl oz relates to the gallon (128 fl oz = 1 gal), the cup (8 fl oz = 1 cup), the tablespoon (2 tbsp = 1 fl oz), and the milliliter (1 fl oz ≈ 29.57 mL). Cocktail recipes universally use fluid ounces.

Visual reference for how the fluid ounce relates to other volume units. Each row links to the full converter for that pair.

See all 15 volume units in matrix view →

• US beverage and soda can sizes (12 fl oz)
• Cosmetic and personal-care product volumes
• US fluid recipes and cocktail measures

• ✓1 US fl oz ≈ 29.6 ml; 1 UK fl oz ≈ 28.4 ml.
• ✓8 US fl oz ≈ 1 US cup ≈ 237 ml.
• ✓Use ml to avoid ambiguity between US and UK fluid ounces.

• ✗Mixing US and UK fluid ounces — 16 fl oz (US) = 473 ml vs. 16 fl oz (UK) = 455 ml.
• ✗Confusing fluid ounce (volume) with avoirdupois ounce (mass).
• ✗Assuming 1 fl oz = 1 oz by weight — only true for pure water and approximately.