How Many Ounces in a Cup?

Almost nothing you buy is labeled in cups

Stores sell liquid in fluid ounces and recipes ask for it in cups, so the useful skill here is reading a label and dividing by 8. The oddest number on the shelf is the 16.9 fl oz water bottle: that's 2.11 cups, or 2 cups plus a little under 2 tablespoons. If a recipe wants 2 cups, the bottle covers it with a swallow left over, and I'd drink that swallow before I'd wash a measuring cup for it.

That odd 16.9 also works out to 499.79 mL, so the bottle is half a liter dressed in American units. If a label prints both numbers, go with whichever one your measuring tool speaks. Set the unit to fluid ounces above and type the number from the label, and the plan for 16.9 reads 2 cups plus 2 tablespoons, about 0.6% over instead of pretending the match is exact.

The 12 oz can

Twelve fluid ounces is exactly 1½ cups, or 24 tablespoons, which makes it the friendliest number on the shelf. Two cans give you 3 cups, and four give you 6. If you need only 1 cup, that's two-thirds of the can, and the other ½ cup stays behind for something else. I'd still pour that cup into a measure, because two-thirds of a can you can't see into is not something anyone can judge by eye.

The 32 oz carton of broth

Four cups. A 32 fl oz carton is one quart, and this is the label I'd commit to memory, because recipes rarely ask for a round carton. Two cups for a risotto uses half of it. Three cups leaves you exactly 1 cup to put away. Past one carton, the arithmetic stays simple: 10 cups of broth is 2½ cartons, so you're buying three. The cups in a quart page takes that further if you're scaling a soup.

"Oz" alone is a different ounce

Read the word on the label. The tables in NIST Handbook 44 treat the fluid ounce as a measure of capacity and the plain ounce as a measure of weight. So "fl oz" is space and everything on this page applies, while "oz" or "net wt" alone generally means weight, and dividing that by 8 tells you nothing useful. The cooking conversion chart covers that difference in full.

Ounces in a cup of flour, sugar or butter

A cup of something dry isn't 8 ounces, and it isn't the same number twice. On the King Arthur chart, a cup of all-purpose flour is about 4¼ ounces by weight (120 grams), granulated sugar about 7 ounces (198 grams), and butter 8 ounces (227 grams). Butter is the one that happens to agree with the fluid figure, and I wouldn't let that coincidence stretch any further.

When can you just empty the bottle?

Labels invite shortcuts, and most of them are harmless. If a stew wants 2 cups of liquid, emptying a 16.9 fl oz bottle adds about 1.8 tablespoons nobody asked for, and I'd take that deal without a second thought. A stew has room for it.

Rice doesn't. There the water is close to being the whole recipe, so I'd get the amount from the rice to water calculator and pour exactly that, whatever the bottle happens to hold. Baking gets the same treatment. On 2 cups, those 1.8 tablespoons come to about 5.6% extra liquid, and I wouldn't hand 5.6% to a cake just to save a rinse.