How Many Ounces in a Cup

Fluid ounces measure volume, ounces measure weight

The short answer is 8. One US cup holds 8 fluid ounces of liquid. The longer answer is that the word ounce covers two different units, and a recipe means one of them depending on what you are measuring.

A fluid ounce is volume, the space something takes up. An ounce on a kitchen scale is weight, or mass. They line up for water and close to it for milk and stock, because those are mostly water: a cup of water weighs 8.3 ounces. They part company for anything with air in it or density above water. A cup of all-purpose flour weighs 4.4 ounces. A cup of honey weighs 12 ounces. Both are 1 cup, and both are 8 fluid ounces of volume.

That is why a recipe that lists flour in ounces and another that lists it in cups can disagree, even when both are right. Weighing is more repeatable, which is why most baking recipes written for experienced cooks give weights. Cups are fine for cooking, where a few grams of onion either way changes nothing.

The calculator above takes a number and a unit, gives you the volume conversions, and then uses the ingredient to turn that volume into weight. Pick the ingredient and it shows both, so you can see exactly how far apart the two ounces are.

The 8 fluid ounce cup and where it comes from

US kitchen volumes nest into each other in a fixed ladder, and every rung is a clean multiple of the one below it.

• 1 tablespoon = 3 teaspoons
• 1 fluid ounce = 2 tablespoons
• 1 cup = 8 fluid ounces = 16 tablespoons = 48 teaspoons
• 1 cup = 236.6 milliliters
• 2 cups = 1 pint, 4 cups = 1 quart, 16 cups = 1 gallon (128 fluid ounces)

One US cup is 236.588 milliliters exactly, which comes from the definition of a US gallon as 231 cubic inches. Food labels round it to 240 milliliters for the Nutrition Facts panel, and most American recipes treat the two as the same. The NIST unit conversion reference is the source for the exact figure.

Outside the United States a cup is not the same thing. The legal metric cup used in Australia, Canada and New Zealand is 250 milliliters, and an older British recipe means 284 milliliters, which is 10 British fluid ounces. A recipe written in cups outside the US is usually metric, so check the origin before you convert.

The one that trips people up most often is the fluid ounce itself. A US fluid ounce is 29.57 milliliters. A British fluid ounce is 28.41 milliliters, and the British pint is 20 fluid ounces rather than 16. If a recipe comes from the UK and the amounts look large, that is why.

Dry cups and liquid cups are different tools

Dry measuring cups and liquid measuring cups measure the same volume but are built for different jobs, and swapping them is the most common source of error in a home kitchen.

A liquid cup filled to the brim with flour holds more than a leveled dry cup, sometimes by 20 percent, because the flour has not been leveled and has not settled. A dry cup used for milk loses the headroom a liquid cup gives you, and it cannot be read at eye level, so the pour is always a guess.

Two habits fix most of it. Read liquid amounts on a flat counter at eye level rather than looking down into the cup, and level dry ingredients with the back of a knife rather than tapping or packing. Packing is only correct when the recipe says packed, as in brown sugar.

What a cup weighs depends on the ingredient

You cannot convert ounces to cups without knowing the ingredient, because the conversion depends on density. The table below gives the weight of 1 level cup for the ingredients people ask about most, using figures from USDA FoodData Central and standard kitchen references.

Flour is the widest trap, because a cup of it can weigh anywhere from 3.5 to 5.5 ounces depending on whether it was scooped from the bag, spooned in and leveled, or sifted. Two bakers using the same "1 cup" of flour can be 25 percent apart, and that is enough to change a cake from tender to tough. A scale removes the whole problem: 125 grams is 125 grams every time.

The USDA FoodData Central database is where these weights come from, and it lists the gram weight per cup for thousands of ingredients. If an ingredient is not in the table above, that is the place to look.

Worked example: 1 cup of all-purpose flour

Take 1 cup of all-purpose flour, which is the default in the calculator above. The output reads like this:

• Volume: 1 cup = 8 fluid ounces = 16 tablespoons = 48 teaspoons
• Metric volume: 236.6 milliliters
• Weight: 4.4 ounces, or 125 grams

So the answer to "how many ounces in a cup of flour" depends on which ounce you mean. It is 8 fluid ounces by volume, and 4.4 ounces by weight. If a recipe says 8 ounces of flour and you measure 1 cup, you have about half of what it asked for.

Change the ingredient to granulated sugar and the volume rows stay identical at 8 fluid ounces and 236.6 milliliters, while the weight jumps to 7.1 ounces, or 200 grams. Change it to honey and the weight is 12 ounces, half again as much as the water in the same cup.

Scale the amount before you convert, not after. Half a cup of flour is 2 fluid ounces of volume and 2.2 ounces of weight, which is 62.5 grams. Doubling a recipe that lists cups is safe, doubling one that lists weights is safer still.

Kitchen conversion table for cups and fractions

These are the fractions that come up most often, with the fluid ounce, tablespoon and milliliter equivalents for each.

A stick of butter is worth memorizing because it crosses both systems: 1 stick is 8 tablespoons, which is 1/2 cup, which is 4 ounces, which is 113 grams. Two sticks is 1 cup, and the wrapper is printed with the marks.

Odd fractions are easier in tablespoons once they get small. A third of a cup is 5 tablespoons plus 1 teaspoon, and two thirds is 10 tablespoons plus 2 teaspoons. Measuring that with a dry cup set means guessing between marks, while a tablespoon set hits it exactly.

Three rules that prevent most conversion mistakes

Three rules cover almost every mistake that shows up in a converted recipe.

• Read the unit in the ingredient list. "8 oz chocolate" means weight, and "8 fl oz milk" means volume. A recipe that says ounces without fl is usually weight.
• Weigh when the recipe is baked. Cups of flour vary by 25 percent between cooks. A $15 scale is the single best baking purchase there is.
• Do not convert a label backwards. A Nutrition Facts panel shows 240 milliliters for 1 cup, and serving sizes are rounded to the nearest 5 or 10 grams, so label math is not precise.

On packaging, the FDA food labeling rules set the rounding for the Nutrition Facts panel, which is why a label can round a cup of water from 237 milliliters to 240. For the exact conversion factors themselves, the NIST unit conversion page is the authoritative source, and the same page covers cups, fluid ounces and liters.

When in doubt, match the system the recipe was written in. An American recipe in cups works best with American cups, and a recipe in grams works best with a scale. Converting mid recipe is where the errors creep in.