How many oz are in a fl oz?

It is commonly abbreviated as fl. oz. (or fl oz), which can mean a singular fluid ounce, or, more commonly, the plural fluid ounces.

An ounce is a unit used in the measurement of weight. (Both ounce and ounces can be abbreviated as oz.) A fluid ounce is used to measure volume (capacity), not weight—specifically, the volume of a fluid (liquid). In everyday conversation, the word ounces is often used instead of saying fluid ounces, as in I just drank 16 ounces of that energy drink. The abbreviation oz. is sometimes used in this way, as in a 20 oz. bottle of water. 

You’ll often see the abbreviation fl. oz. on the labels of containers that contain liquid or some other kind of non-solid, such as a can of soda or a bottle of moisturizer, to indicate how much stuff the container contains. It is also seen in recipes.

Fluid ounces are used in the United States Customary System and the British Imperial System of measurement.

In the Customary System, there are 8 fluid ounces in a cup and 16 fluid ounces in a pint. There are 20 fluid ounces in an Imperial pint.

A fluid ounce is equal to 29.57 milliliters (1 milliliter is equivalent to 0.033815 of a fluid ounce.)

Cory is the Associate Food Editor at Kitchn. Previously an editor at Food Network Magazine, Cory loves making cold brew at home, trying out new soup recipes, zhuzhing up Trader Joe's finds, and putting everything seasoning on something. When he's not in the kitchen, you can find him looking for a new crime doc to watch with a glass of Invivo X, SJP's sauvignon blanc nearby.

updated Jun 23, 2022

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If you’ve done any significant amount of cooking or baking (particularly baking!), then it’s pretty likely you’ve seen some ingredients in the recipe written out in ounces. (Check out these recipes for a tasty layer cake and sugar cookies for two examples).

But when you’re cooking, it’s important keep in mind that there are different types of ounces: fluid ounces and ounces by weight. These two terms are both a form of measurements for foods, though they have completely different functions.

Are Fluid Ounces the Same as Ounces?

To put it simply: No, fluid ounces are not the name same as ounces. Both fluid ounces and ounces represent a unit of measurement, but they are quite different. Fluid ounces, as the name might imply, are specifically meant to measure volume (often of liquid ingredients like water), while ounces measure weight, usually of solid ingredients like all-purpose flour.

Credit: Joe Lingeman

Ounces Measure Weight

Ounces are a unit used to measure weight. This measurement is most often used with dry ingredients, but can also be used for things like honey or yogurt. When a recipe calls for ounces, it’s referring to a specific weight. You may notice baking recipes written in ounces instead of cups — this is because measuring ingredients by weight is more accurate and a better way of getting more equal measurements. The best way to measure ounces is by using a kitchen scale.

Credit: Photo: Joe Lingeman; Food Styling: Jessie Yu Chen

Fluid Ounces Measure Volume

Fluid ounces are a unit used to measure volume, or how much space something takes up. This measurement is used for liquid ingredients, like water or milk. When a recipe calls for fluid ounces, you should use a glass measuring cup with measurements on it — this is the most accurate way to measure a liquid ingredient in baking.

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Are Ounces and Fluid Ounces Interchangeable?

If you’re truly looking to prepare a baking recipe in the most accurate way possible, then you should not use fluid ounces and ounces interchangeably. On most occasions, fluid ounces and ounces (weight) are not interchangeable because different ingredients have different weights and take up different amounts of space.

Think of one cup of flour and one cup of tomato sauce; they both occupy the same volume of space (i.e., 8 fluid ounces), but they have very different weights (about 4 ounces for the flour, and about 7.9 ounces for the tomato sauce). One exception to this, however, is water. Water happens to equal both 8 fluid ounces (in volume) and 8 ounces (in weight). All other ingredients should be measured out either by weight or volume. Be sure to pay close attention when reading your recipe to make sure you’re measuring correctly!

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