You’re standing over a bowl of brownie batter and the recipe suddenly demands precision. You need to know how many ounces in 2/3 cup right now, but your brain is doing that weird glitch where fractions and decimals refuse to get along. Honestly, it happens to the best of us. Most people assume there's one simple number that solves this, but if you’ve ever had a cake come out like a brick or a sauce that refused to thicken, you know the truth is a bit more slippery.
Measuring isn't just about filling a plastic scoop. It's about physics.
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If you are measuring water, milk, or oil, the answer is technically 5.33 fluid ounces. But wait. Try measuring flour that way and you are going to have a bad time. Liquid ounces and dry ounces are different beasts entirely, and confusing the two is exactly why Grandma’s cookies always taste better than yours. She knew that 2/3 of a cup isn't a "one size fits all" measurement.
Why 5.33 Ounces in 2/3 Cup is Only Half the Story
We have to talk about the "fluid" part of fluid ounces. In the US Customary System, a full cup is 8 fluid ounces. Math tells us that two-thirds of eight is 5.3333... and so on. You can't really measure .33 of an ounce in a standard kitchen unless you’re using a laboratory-grade pipette. Most home cooks just round it. They eyeball it.
They shouldn't.
Liquid measuring cups are designed with extra space at the top so you don’t spill your milk on the way to the bowl. Dry measuring cups are meant to be leveled off with a knife. If you use a liquid cup for 2/3 cup of flour, you’re almost certainly going to pack it down or underfill it, leading to a massive discrepancy in weight. This is where the ounces in 2/3 cup conversation gets messy.
Weight versus volume.
A 2/3 cup of honey weighs significantly more than 2/3 cup of panko breadcrumbs. If you're looking at a recipe from the UK or Australia, things get even weirder because their "cup" is 250 milliliters, while a US cup is roughly 240 milliliters. That small 10ml difference might not matter for a stew, but for a soufflé? It’s a disaster waiting to happen.
The Dry Ingredient Trap
Let’s get specific.
If you scoop 2/3 cup of all-purpose flour straight from the bag, you’re likely cramming about 3.5 to 4 ounces of weight into that space. However, if you sift that flour first, that same 2/3 cup might only weigh 2.8 ounces. This is why professional bakers like Joanne Chang or Peter Reinhart beg people to buy a digital scale. They don't care about "cups." They care about grams and ounces.
Specifically, weight ounces.
When you see a recipe asking for ounces in 2/3 cup, you have to look at the context. Is it a liquid? Use 5.33 fl oz. Is it a dry powder? You’re likely looking at somewhere between 2.5 and 3.5 weight ounces depending on the density. Sugar is heavier than flour. Cocoa powder is lighter than both. It’s a chaotic mess if you don't have a scale.
Common Kitchen Conversions for 2/3 Cup
- Water or Milk: 5.33 fluid ounces.
- Granulated Sugar: Roughly 4.7 ounces (weight).
- All-Purpose Flour: Roughly 3.1 ounces (weight, depending on the "scoop" method).
- Chocolate Chips: About 4 ounces (weight).
- Butter: 5.33 ounces (which is 10.6 tablespoons, or about 1 and 1/3 sticks).
Breaking Down the Math (The Painless Way)
Most of us aren't doing long division while we’re sautéing onions. You just need a quick reference.
Since one cup is 16 tablespoons, 2/3 of a cup is 10 tablespoons plus 2 teaspoons. That is the "Golden Ratio" for most home cooks. If you lose your 2/3 measuring cup—which always seems to be the one that goes missing in the junk drawer—just grab the tablespoon and start counting. 10.66 tablespoons is the target.
Do 10 tablespoons and 2 teaspoons. Close enough.
King Arthur Baking, arguably the gold standard for American home baking, uses a specific weight for flour: 120 grams per cup. In that world, ounces in 2/3 cup of flour comes out to exactly 80 grams, or about 2.82 ounces. If you use the "dip and sweep" method (dipping the cup into the flour), you’ll end up with way more than 2.8 ounces. You’ll end up with a dry, crumbly mess.
The Fluid Ounce vs. Weighted Ounce Nightmare
It’s an old riddle: which weighs more, a pound of lead or a pound of feathers? They weigh the same. But 2/3 cup of lead and 2/3 cup of feathers? Huge difference.
The US is one of the few places that still clings to volume-based measuring for dry goods. In most of Europe, you wouldn't ask how many ounces in 2/3 cup; you’d just see "150g" on the page.
Fluid ounces measure volume (how much space something takes up).
Weight ounces measure mass (how heavy it is).
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Honey is a great example. If you pour 2/3 cup of honey, you have 5.33 fluid ounces of volume. But if you put that honey on a scale, it will weigh roughly 8 ounces. It’s dense. It’s heavy. If a recipe calls for "8 ounces of honey," and you use an 8-ounce measuring cup, you’ve actually just added about 12 ounces of honey. You’ve ruined the recipe.
Always check if the recipe says "net wt" (net weight) or "fl oz" (fluid ounces). If it just says "ounces," and it's a liquid, assume fluid. If it's a solid, assume weight.
Practical Tips for Getting 2/3 Cup Right
Stop guessing.
First, get a dedicated liquid measuring cup (the glass kind with a spout) and a set of nesting dry measuring cups (the metal kind you level off). Never swap them.
Second, if you're dealing with "sticky" ingredients like peanut butter or molasses in a 2/3 cup measurement, spray the inside of the cup with a little non-stick cooking spray first. The ingredient will slide right out, ensuring you actually get all 5.33 ounces into the bowl instead of leaving half an ounce stuck to the sides.
Third, remember that 1/3 cup is 2.66 fluid ounces. So, 2/3 cup is just that doubled. If you only have a 1/3 cup measure, just fill it twice. It’s actually more accurate for some people because it’s easier to level off a small cup twice than to eyeball a line on a large glass pitcher.
Understanding the "Scant" and "Heaping" Terms
Sometimes you'll see a recipe call for a "scant 2/3 cup." This is code for "a little bit less than 5.33 ounces." It usually means the developer found that a full 2/3 cup made the dough too wet or too sweet. Aim for about 5 ounces flat.
A "heaping" 2/3 cup? That’s only for dry goods. You can’t heap a liquid unless you’re some kind of physics wizard. A heaping cup of flour can easily add an extra half-ounce of weight, which is enough to change the texture of a delicate sponge cake.
Actionable Next Steps for Better Accuracy
Stop relying on the "eyeball" method for your ounces in 2/3 cup conversions. It’s the fastest way to inconsistent results.
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- Buy a digital kitchen scale. This is the single biggest upgrade you can make. Switch your recipes to grams or weight ounces. It eliminates the "is this 2/3 cup packed or loose?" debate entirely.
- Memorize the 10+2 rule. 10 tablespoons and 2 teaspoons equals 2/3 cup. It’s the easiest way to measure when your specific 2/3 cup tool is dirty or missing.
- Check the "Standard." Verify if your recipe is using US Customary (8oz cup) or Metric (250ml cup). Most modern web recipes are US-based, but older cookbooks or international blogs will throw your ratios off by about 4%.
- Level your solids. Use the back of a butter knife to sweep across the top of your dry measuring cup. Never shake the cup to level it, as this settles the contents and increases the weight.
- Read the label. If you're using a canned good (like pumpkin puree), the ounces listed on the can are weight ounces, not fluid ounces. A 15-ounce can of pumpkin is not 1.8 cups; it's actually closer to 1.5 cups because pumpkin is dense.
Precision in the kitchen feels like a chore until you taste the difference. When you stop treating "2/3 cup" as a suggestion and start treating it as a specific 5.33-ounce target, your cooking moves from "okay" to "professional."