Ounces to Fluid Ounces (oz to fl oz)

Divide the weight in ounces by what one fluid ounce of the ingredient weighs. The divisor in the formula above belongs to water. For other foods, choose the ingredient in the converter and it swaps in the right figure.

Butter is the easy case, since one ounce of it takes up about 1 fluid ounce. A 4 oz stick of butter is marked as 1/2 cup, which is 4 fluid ounces, so its weight and volume line up. Granulated sugar packs less tightly, so 6 oz of it fills about 6.8 fluid ounces.

For the reverse trip, from a volume to a weight, use the fluid ounces to ounces converter.

The weight ounce is the same in the US and the UK, but the fluid ounce is not. As the table below shows, the British (imperial) fluid ounce is the smaller of the two.

That gap changes the water math. An imperial fluid ounce of water weighs 1.002 ounces, so in a British recipe that uses fluid ounces the two kinds of ounce almost match for water. With US fluid ounces they drift further apart, which is why the formula above divides by a number a little over one.

A scale ounce tells you how heavy something is, and a fluid ounce tells you how much room it needs. The two only track each other for liquids close to water, such as milk.

Light, bulky foods need far more room per ounce. An ounce of whole blueberries fills about 1.53 fluid ounces, and 8 oz of shredded cheese fills about 2 cups. When a recipe lists cheese or flour in ounces, it usually means weight, not a mark on a measuring cup.

US food labels follow a federal rule. Liquids are declared by fluid measure, and solid, semisolid or viscous foods by weight, using the term "net weight" (21 CFR 101.7).

So "fl oz" on a bottle of juice gives its volume, while "net weight" in ounces on a jar of peanut butter gives its weight. The rule allows exceptions where a trade custom is firmly established, so read the words next to the number, not just the "oz".