Oz to Milliliters - How Many ml in a Fluid Ounce?

What is a fluid ounce?

A fluid ounce is a unit of volume, not weight. One US fluid ounce equals exactly 29.5735295625 ml. The name comes from the weight of one ounce of water, but the two measurements diverged centuries ago. Today, "ounce" can mean weight (oz) or volume (fl oz). In cooking and drink recipes, it almost always means fluid ounces.

The formula is straightforward: milliliters = fluid ounces x 29.57. To reverse: fluid ounces = milliliters divided by 29.57. For quick math, round to 30 ml per fluid ounce. The error is less than 1.5%, which is fine for kitchen use.

US fluid ounce vs. UK fluid ounce

The US fluid ounce (29.57 ml) and the UK fluid ounce (28.41 ml) are not the same. The difference is about 1.16 ml per ounce. For a single shot, that barely matters. For a full pint, it adds up. A US pint is 16 fl oz (473 ml). A UK pint is 20 fl oz (568 ml). So a British pint is actually bigger than an American pint - even though each British ounce is slightly smaller.

When you see "fl oz" on a US product label, it means the US fluid ounce. On a UK product, it means the Imperial fluid ounce. If a recipe does not specify, assume US for American sources and Imperial for British sources. Most modern British recipes use milliliters directly.

Common bottle and container sizes

Understanding fluid ounces helps you decode US product labels. A standard soda can holds 12 fl oz (355 ml). A typical water bottle is 16.9 fl oz (500 ml). A wine bottle holds 25.4 fl oz (750 ml). A US gallon of milk is 128 fl oz (3,785 ml).

In the bar world, a standard shot is 1.5 fl oz (44 ml) in the US. A jigger holds 1.5 fl oz on one side and 0.75 fl oz (22 ml) on the other. Cocktail recipes almost always use fluid ounces. Knowing that 1 fl oz is about 30 ml makes mental conversion easy.

Fluid ounces in cooking

Many American recipes list liquids in fluid ounces instead of cups. "Add 6 fl oz of cream" is clearer than "3/4 cup of cream" for some cooks. The relationship is simple: 8 fl oz = 1 cup. So divide the ounce value by 8 to get cups, or multiply cups by 8 to get ounces.

For small amounts, fluid ounces connect directly to tablespoons. One fluid ounce equals 2 tablespoons. One tablespoon equals 0.5 fl oz. This is useful when a recipe calls for "1 fl oz vanilla extract" - that is 2 tablespoons.

Ounces vs. fluid ounces - weight vs. volume

This is a common source of confusion. An ounce (oz) measures weight: 1 oz = 28.35 grams. A fluid ounce (fl oz) measures volume: 1 fl oz = 29.57 ml. For water, the numbers are close because water is dense. One fluid ounce of water weighs almost exactly one ounce.

For other liquids, the gap widens. One fluid ounce of honey weighs about 1.5 oz because honey is denser than water. One fluid ounce of oil weighs about 0.95 oz because oil is lighter. In recipes, "ounce" without "fluid" usually means weight. "Fluid ounce" or "fl oz" always means volume.