The RIGHT Way to Measure Your Bra Size

how to measure your bra size chicago petite

For most of my adult life, I’d been laboring under the impression that I was a solid 34A. And throughout all that time, I always felt kind of embarrassed about my small boobies. I wore padded bras and did what I could to make them look a little fuller (sometimes even pulling out the ol’ double bra trick), but of course that didn’t change the fact.

Here’s the thing: this is a story about perception creating reality. My boobs are actually kinda big. I just didn’t know it until recently.

See, ever since I was old enough to wear a bra, I thought that you had to measure your bra size by using the same formula that every woman’s magazine seems to publish. You know which one. First, you measure under your bust and add 4″ to get your band size. Then you measure the fullest part of your chest. Take that measurement and subtract your band size measurement. Well, for me, that always came out to 34A.

I didn’t ever question the fact that my boobs never seemed to squeeze into the cups the way they should. I simply assumed that was the way they were supposed to look. That is, until I read How to Get Dressed by Alison Freer.

In it, she explained the true formula you should use for measuring your bra size. I corroborated her finding with r/ABraThatFits, and unbelievably, I found out that I am a 30-FREAKING-DD.

At first, I thought something must be terribly off. How could possibly be rocking a pair of double-d’s? It made no sense whatsoever. I mean, I could certainly stuff myself into an A cup, so this had to be a mistake. I ordered a couple of bras in my new size, and lo, they fit perfectly. I almost couldn’t believe my eyes! I slipped a tight t-shirt over my new brassiere and, to my astonishment, nothing showed through. No bumps, no bad seams—it fit like a dream.

If you’re anything like me, chances are you’re wearing the wrong size bra, too. Here’s how to fix it:


According to Freer, the proper way to measure your bra size goes like this: measure under your bust with a cloth measuring tape. Make sure it’s snug, and use a mirror to make sure it’s sitting correctly. This is your band size. Now, measure the fullest part of your chest, again, making sure the tape is properly aligned and a little snug (but not so much that it squashes your boobs). Subtract your band size from this measurement. The difference will tell you what your cup size is.

Difference of 1″ = A

Difference of 2″ = B

Difference of 3″ = C

Difference of 4″ = D

Difference of 5″ = DD

Difference of 6″ = DDD/E

Difference of 7″ = DDDD/F

If you’d like a very comprehensive calculator, I highly recommend this one.


It causes all kinds of fit issues when you try to measure your bra size. Like I said, for many years, I assumed that my bras fit me, even though there were lumps and bulges all over the place. With the old formula, you end up with a band size that’s way too big. This means it’s more liable to ride up in the back, which equals less support (boo!). On the flip side, your cups are too small, so you won’t be able to get everything into them.


Glad you asked! My whole adult life I’ve been shopping at Victoria’s Secret, but now that I’m armed with my new size, I’ve been trying out some higher-end gear. One brand I really like is Natori. They carry some hard-to-find sizes (such as my 30DD), and their bras are GORGEOUS. Seriously, they look so good. The only problem I’ve had with them is that depending on the style of bra, they can run small, so be sure to check the reviews and buy a couple to try on. I would also highly recommend ThirdLove. I just bought one and it fits and feels really nice. Their selection is a little bit limited when it comes to rarer sizes, but if you’re okay with sister sizing (see below), you shouldn’t have trouble finding one.

A note on sister sizing: if you have a small band size like me, you will definitely have a hard time finding cute bras in your size. However, there is such a thing as sister sizing. This means you can go up a band size and down a cup size and still have the same volume cup. So for me, 32D is a sister size for 30DD. 32D is a LOT easier to find, so I’m willing to put up with a slightly larger band size.

So that’s really how to measure your bra size! Give this new formula a whirl—you might be just as surprised as me!


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