How Many Ounces in a Cup?

The Short Version

One US cup holds exactly 8 fluid ounces. Pour water into a standard measuring cup up to the 1-cup line, and you have 8 fl oz. Done. But the real question most people stumble on is: are fluid ounces and dry ounces the same thing? They are not, and confusing them is the single most common baking mistake in American kitchens.

Fluid Ounces vs. Dry Ounces: Two Different Animals

A fluid ounce measures volume -- how much space something takes up. A dry ounce measures weight -- how heavy something is. They share a name because, centuries ago, one fluid ounce of water happened to weigh roughly one ounce on a scale. Water is the exception where both numbers align. Almost nothing else does.

Consider flour. One cup of all-purpose flour weighs about 4.25 dry ounces, not 8. A cup of honey? Around 12 ounces by weight. A cup of popcorn kernels weighs about 7.5 ounces. Same volume, wildly different weights. The density of the ingredient decides everything.

Rule of thumb: if a recipe says "8 oz of milk," it almost certainly means fluid ounces -- grab your liquid measuring cup. If it says "8 oz of chocolate chips," it means weight -- grab your kitchen scale.

When It Matters Most

Cooking is forgiving. Adding a splash more broth to a soup won't ruin dinner. Baking is chemistry. If a brownie recipe calls for 4 oz of melted butter and you measure 4 fluid ounces instead of weighing 4 ounces, you'll get roughly 7 tablespoons instead of 8. That 12% error can mean the difference between fudgy and cakey. Professional pastry chefs weigh everything in grams for this reason.

US Cups vs. UK Cups vs. Metric Cups

The world has not agreed on how big a "cup" should be. Here is the breakdown:

• US customary cup: 8 fl oz (236.6 mL)
• US legal cup (used on nutrition labels): 8.12 fl oz (240 mL)
• Imperial (UK) cup: 10 fl oz (284.1 mL) -- about 20% larger
• Metric cup (Australia, New Zealand): 8.45 fl oz (250 mL)

This matters if you follow a recipe from a British cookbook. Their cup of flour is a full 20% more than an American cup. Scale accordingly or you'll end up with a brick instead of a scone.

A quick conversion cheat: multiply US cups by 1.2 to get Imperial cups, or multiply by 236.6 to get millilitres.

Practical Measuring Tips

For Liquids

Use a clear glass or plastic measuring cup with a spout. Set it on a flat surface. Pour your liquid in, then bend down so your eyes are level with the markings -- reading from above makes the liquid look higher than it is (a physics effect called the meniscus). For sticky liquids like honey or maple syrup, spray the cup with cooking oil first. The liquid slides right out and you get a full, accurate measurement.

For Dry Ingredients

Spoon the ingredient into a dry measuring cup until it mounds above the rim, then sweep a straight edge (the back of a butter knife works perfectly) across the top. Never pack flour by scooping the cup directly into the bag -- that compresses the flour and can give you up to 30% more than intended. Sugar is the opposite: brown sugar is always packed firmly, while granulated sugar is spooned and leveled.

Ounce Conversions for Common Ingredients

Because density varies, here is what 1 cup actually weighs for ingredients you reach for every day:

• Water: 8 oz
• Whole milk: 8.6 oz
• All-purpose flour: 4.25 oz
• Granulated sugar: 7 oz
• Butter: 8 oz (2 sticks)
• Vegetable oil: 7.7 oz
• Honey: 12 oz
• Rolled oats: 3 oz

Print this list and tape it inside a cabinet door. It saves more time than any kitchen gadget.

Why the US Still Uses Ounces

The United States, Liberia, and Myanmar are the only countries that have not officially adopted the metric system. Congress actually passed the Metric Conversion Act in 1975, but it was voluntary. Forty years later, American grocery stores still sell milk by the gallon and butter by the pound. The result is a hybrid mess: scientists use metric, nutritionists use metric on labels but reference household measures, and home cooks use cups, tablespoons, and ounces. If you cook international recipes often, investing in a dual-unit kitchen scale (grams and ounces) eliminates the conversion problem entirely.

Quick Reference Table

Pin this on your fridge:

• 1 cup = 8 fl oz = 16 tablespoons = 48 teaspoons
• 3/4 cup = 6 fl oz = 12 tablespoons
• 2/3 cup = 5.33 fl oz = 10 tbsp + 2 tsp
• 1/2 cup = 4 fl oz = 8 tablespoons
• 1/3 cup = 2.67 fl oz = 5 tbsp + 1 tsp
• 1/4 cup = 2 fl oz = 4 tablespoons