You’re standing there with flour on your hands, staring at a recipe that calls for doubling a specific amount, and suddenly your brain just freezes. It happens to the best of us. You need to figure out 2 3 cup plus 2 3 cup, but for some reason, the math isn't clicking while the oven is preheating and the kids are screaming in the next room. Math is hard. Fractions are worse. Honestly, most people just start guestimating, which is exactly how you end up with a cake that has the structural integrity of a brick.
The short answer? It is $1$ and $1/3$ cups.
But if you’re looking for the "why" or how to actually measure that out when you can’t find your one-third measuring cup, there’s a bit more to the story. Most kitchen sets come with a standard array: 1 cup, 1/2 cup, 1/3 cup, and 1/4 cup. Notice anything missing? There is almost never a 2/3 measuring cup in a standard retail set. This creates a weird logistical hurdle every time you hit this specific measurement. You end up doing a frantic dance of scooping and leveling that would make a chemist sweat.
The Raw Math of 2 3 cup plus 2 3 cup
Let’s look at the numbers. When you add $2/3$ and $2/3$, you keep the denominator (the bottom number) the same because the "size" of the pieces hasn't changed. You just add the numerators (the top numbers). 2 plus 2 is 4. So, you have $4/3$ cups.
Since $3/3$ equals a whole cup, you take that 3 out of the 4, leave the remainder, and you get $1$ and $1/3$ cups.
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Simple, right? On paper, sure. In a bowl of sticky molasses? Not so much.
If you are working with a liquid measuring cup—those glass Pyrex ones we all have—finding the $1$ $1/3$ line is usually easy. But if you are using dry nesting cups, you’re basically forced to use the $1/3$ cup scoop four times. Or, if you’re feeling bold, you use the 1-cup measure once and then the 1/3 cup once.
Why This Specific Measurement Ruins Your Baking
Baking is chemistry. It’s not like making a stew where "a little extra" broth just makes it more flavorful. If you mess up the ratio of flour to fat or liquid, the protein structure changes.
When people try to eyeball 2 3 cup plus 2 3 cup, they often over-measure. They scoop the $1/3$ cup four times but don't level it off perfectly. By the fourth scoop, you’ve actually added an extra tablespoon or two of flour. That sounds like nothing. It isn't. According to King Arthur Baking, a single tablespoon of extra flour can make cookies dry and crumbly instead of chewy.
Precision matters.
Think about the physical space. Four scoops of a 1/3 cup versus one scoop of a 1-cup and one of a 1/3 cup. Every time you dip that plastic or metal cup into the flour, you are compacting it. Professional bakers like Stella Parks (Bravetart) or Claire Saffitz often scream into the void about using scales for this exact reason.
Converting to Tablespoons: The Secret Hack
If you lose your 1/3 cup down the garbage disposal—which happens more than you'd think—you need a backup plan.
There are 16 tablespoons in a cup.
There are 5 tablespoons plus 1 teaspoon in 1/3 of a cup.
So, if you are calculating 2 3 cup plus 2 3 cup, you are looking at a total of 10 tablespoons and 2 teaspoons, plus whatever makes up that extra 1/3 cup. Actually, let's make it easier.
1 cup = 16 tablespoons.
1/3 cup = 5.33 tablespoons.
Total = 21.33 tablespoons.
Does anyone actually want to measure out 21 tablespoons? No. That sounds like a special kind of hell. But if you’re stuck with only a tablespoon set, knowing that 2/3 of a cup is roughly 10 and a half tablespoons can save your recipe in a pinch.
What About Ounces and Milliliters?
Sometimes the recipe switches units on you. It’s annoying.
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In the US, we use fluid ounces. A cup is 8 ounces.
So, $1$ and $1/3$ cups is approximately 10.67 fluid ounces.
In the metric system, which actually makes sense, a cup is roughly 236.5 milliliters.
That means 2 3 cup plus 2 3 cup is about 315 milliliters.
If you have a scale, just use grams. Seriously. 1/3 cup of flour is roughly 40-45 grams depending on how you scoop it. So you’d be looking for about 170-180 grams. It's much faster than washing four different measuring cups because you didn't want to do the math in your head.
The "Doubling" Trap
A lot of people search for this because they are doubling a recipe that originally called for 2/3 cup.
Be careful here.
Doubling a recipe isn't always as simple as $x$ times 2. While the volume of $2/3$ cup plus $2/3$ cup stays the same, the surface area of your pan might not. If you double a brownie recipe that uses 2/3 cup of oil, and you end up with $1$ $1/3$ cups of oil, you better make sure you aren't trying to bake it all in the same 8x8 pan. It won't cook in the middle.
Also, spices. Don’t always double the spices or the salt just because you doubled the main volume. Sometimes $1$ $1/3$ cups of the "main" ingredient only requires 1.5 times the salt. Taste as you go.
Common Substitutions if You're Short
Let's say you realize you need $1$ $1/3$ cups of milk, but you only have $2/3$ cup left in the carton.
You’re short by exactly 2/3 cup.
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You can often sub half-and-half or even water in a cake if the fat content is high enough elsewhere. But don't just guess. If you're missing that second 2/3 cup, you're missing half of your liquid. That's a disaster.
Actionable Steps for Perfect Measurements
Stop guessing.
First, get a kitchen scale. They cost fifteen dollars and will change your life. You’ll never have to worry about adding $2/3$ and $2/3$ again because you’ll just keep pouring until the number on the screen hits the right weight.
Second, if you're stuck with cups, use the "Spoon and Level" method. Use a spoon to fill the 1/3 cup and then scrape the top flat with a knife. Do this four times for your total.
Third, memorize the big three:
- 3 teaspoons = 1 tablespoon.
- 4 tablespoons = 1/4 cup.
- 16 tablespoons = 1 cup.
If you have these burned into your brain, you can navigate any weird fraction the internet throws at you. You won't be the person standing in the kitchen staring at a 1/2 cup measure wondering if you can just "fill it a little bit over the top" to make it 2/3. (Spoiler: You can't, and it won't work).
Measure twice. Bake once. And always remember that $4/3$ is just $1.33$.