You're standing in the kitchen. Flour is everywhere. You’ve got a half-written recipe that calls for how many oz in 1 1/3 cup and honestly, the math just isn't mathing. It happens to the best of us. Most people assume that if a cup is 8 ounces, they can just eyeball the rest. But baking is basically a science experiment where you get to eat the results, and precision matters more than you might think.
The short, direct answer is that 1 1/3 cups is equal to 10.67 fluid ounces.
But wait. There’s a catch. Or rather, several catches that usually ruin a perfectly good sourdough or a batch of cookies. Are you measuring water or are you measuring flour? Because in the world of US customary measurements, "ounces" is a word that works overtime. We use it for volume (fluid ounces) and we use it for weight (avoirdupois ounces). If you mix those up, your cake is going to end up looking like a brick or a puddle.
The Math Behind the Measurements
Let's break it down simply. One standard US cup is 8 fluid ounces. If you take that 8 and add a third of another cup, you're looking at 8 plus 2.666... and so on. We usually round that to 10.67 for the sake of sanity.
It sounds easy. It’s not.
If you are using a dry measuring cup—the kind you scoop with—you are measuring volume. If you put that same 1 1/3 cup of flour on a digital scale, it’s not going to weigh 10.67 ounces. Not even close. Wheat flour usually weighs about 4.25 ounces per cup. So, 1 1/3 cups of flour actually weighs roughly 5.6 ounces. See the problem? This is where recipes go to die.
Why Your Liquid Measuring Cup Is Lying to You
Take a look at your glass measuring pyrex. It has lines for thirds. But have you ever noticed that if you fill it to the 1 1/3 mark while holding it in the air, it’s always wrong? You have to set it on a flat surface. Get your eye level right down there with the meniscus—that little curve the water makes.
If you’re measuring 10.67 ounces of milk, you need that liquid measuring cup. If you use the "nested" plastic cups meant for dry ingredients, you’ll likely spill some or under-fill it because surface tension is a fickle thing.
Dry vs. Liquid: The Great Kitchen Debate
In the UK and most of the world, they’ve mostly abandoned this madness and just use grams. It’s smarter. Seriously. But here in the States, we’re stuck with the system we have.
When a recipe asks how many oz in 1 1/3 cup, it is almost always referring to fluid ounces if the ingredient is a liquid. If it’s a dry ingredient, the recipe is technically asking for a volume measurement, but it’s much better to translate that to weight.
Let’s look at some common kitchen staples. If you need 1 1/3 cups of these, here is what the weight actually looks like compared to the 10.67 fluid ounce volume:
- Granulated Sugar: This is dense. 1 1/3 cups is about 9.3 ounces.
- Confectioners' Sugar: This is fluffy. 1 1/3 cups (sifted) is only about 5.6 ounces.
- Uncooked Rice: Roughly 9.1 ounces.
- Honey or Molasses: These are heavy hitters. You’re looking at nearly 16 ounces in weight for 1 1/3 cups of volume.
I remember once trying to make a massive batch of royal icing. I assumed an ounce was an ounce. I dumped ten ounces of powdered sugar in, thinking I was following the fluid ounce measurement. The result was a soup that wouldn't have hardened if I’d left it in the Sahara for a week.
How to Get 1.33 Cups Without the Guesswork
Maybe you don't have a 1/3 measuring cup. Maybe it’s lost in that one junk drawer we all have. You can actually build 1 1/3 cups using other tools.
You can use a 1-cup measure and then add 5 tablespoons plus 1 teaspoon. That is the mathematical equivalent. Most people don't realize that 3 teaspoons make a tablespoon, and 16 tablespoons make a cup. It's a weird, archaic system, but it works once you memorize the "magic numbers."
If you’re using a scale, which you absolutely should be doing if you bake more than once a year, just set it to ounces. But make sure you know if your recipe was written by someone using the "dip and sweep" method for flour or the "spooned and leveled" method.
The "dip and sweep" (shoving the cup into the flour bag) packs the flour down. You can end up with 20% more flour than the recipe intended. That’s the difference between a moist muffin and something you could use as a hockey puck.
Real-World Conversions You’ll Actually Use
Let’s talk about the 10.67 oz figure again. Where does it actually show up?
If you are buying a can of soda, it's 12 ounces. So 1 1/3 cups is just a little bit less than a full can of Coke. If you have a standard small coffee mug, it usually holds about 8 to 10 ounces. So, 1 1/3 cups will likely overflow that mug.
In professional kitchens, chefs like Julia Child or Jacques Pépin often emphasized that while measurements are a guide, the "feel" matters. But they were also masters of the technical side. They knew that how many oz in 1 1/3 cup was a question of fluid volume.
Common Mistakes to Avoid
- The "Close Enough" Scooping: Never use a coffee mug as a measuring cup. Mugs are not standardized. A "cup" of coffee is often actually 6 ounces in the world of carafe markings, but the mug itself might hold 12.
- Ignoring the Ingredient Density: I can't stress this enough. If you’re measuring 1 1/3 cups of chocolate chips, they don't fill the space perfectly because of the gaps between the chips.
- The Temperature Factor: Cold liquids are slightly denser than hot ones. For most home cooking, this won't ruin your dinner, but for high-level confectionery, it matters.
King Arthur Baking, which is basically the gold standard for US baking advice, suggests that for flour, a "cup" should be 120 grams. If we do the math for 1 1/3 cups, you should be aiming for 160 grams. If you convert that back to weight ounces, it’s 5.64 ounces.
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Compare that to our 10.67 fluid ounce number. It's almost double! This is exactly why people get frustrated with their ovens.
The Tools of the Trade
If you really want to stop worrying about how many oz in 1 1/3 cup, buy a digital scale. They cost fifteen bucks. It's the single best investment you can make for your kitchen.
If you refuse to go digital, at least get a decent set of stainless steel measuring cups that includes the "odd" sizes. Most cheap sets only give you 1/4, 1/2, and 1. Finding a set with a 2/3 and a 3/4 cup measure saves you so much mental math. For 1 1/3 cups, you can just use the 2/3 cup measure twice. Easy. No brain power required.
Actionable Steps for Your Next Recipe
When you see 1 1/3 cups in a recipe, stop and look at the ingredient.
- If it's liquid (water, oil, milk, broth): Grab your clear liquid measuring cup. Fill it to the 1 1/3 line (which is just over 10.5 ounces). Check it at eye level.
- If it's dry (flour, sugar, cocoa): Use the "spoon and level" method. Spoon the ingredient into a 1-cup measure and a 1/3-cup measure. Level it off with a flat knife. Don't shake it down.
- If it's "sticky" (peanut butter, honey): Lightly spray your measuring cup with non-stick oil first. It will slide right out, ensuring you actually get the full 10.67 fluid ounces worth of volume into your bowl instead of leaving half an ounce stuck to the plastic.
Understanding these nuances makes you a better cook. It moves you from just following a script to actually understanding the "why" behind the instructions.
Next time you're doubling a recipe and you have to figure out what 1 1/3 cups times two is (it's 2 2/3 cups, or 21.33 ounces), you'll have the confidence to just do it. No more panic-searching your phone with floury fingers.
The reality is that 10.67 ounces is your magic number for liquids. For everything else, trust your scale over your eyes. Accurate measuring is the secret hurdle between a "pretty good" meal and a "can I have the recipe?" meal. Keep your ratios tight, keep your scale calibrated, and stop eyeballing the 1/3 cup mark. Your taste buds will thank you.