How Bra Sizing Works

How Bra Sizing Works


I'm going to tell you something that may blow your mind:

DDs can be small and B cups can be big. In fact, some DDs are smaller than some Bs.

That's because there's two parts to bra sizes: the band size and the cup size. You knew that though. What you may or may not know is that cup size is *relevant* to band size. The bigger the band size the bigger the cup and vice versa!

Let's start with the basics.

To find your bra size you measure directly under your breasts. You are basically measuring the circumference of your ribcage right beneath your boobs, where the band of the bra sits.

To measure the bust you measure around the fullest part of your breasts.

Here's where it gets tricky.

Some fitters add 5" to the underbust measurement and round to the nearest even number. Some don't add anything.

Either way, you subtract the band size measurement from the cup size measurement.

A one inch difference = A

2" = B

3" = C

And so forth and so forth and yes, it goes on forever.

According to the first method I'm a 32A. According to the second I'm a 28D.

I wear a 32B, which fits just fine in the band and the cups are slightly snug but a 32C would be a bit too big.

My boobs are awfully small but yes, I'm technically a D cup according to some fitters.


Remember when I said cup size is relevant? Allow me to demonstrate.

A 32DD holds the same cup volume as a 34D, and a 36C, and a 38B, and a 40A.

A 36AA holds the same as a 34A, and a 32B.

Every time you go up a band size you go down a cup size and vice versa.

So in these discussions of "what's the best cup size?" You all aren't talking about the same thing. If you think C cup is ideal, well, a 28C is the same cup size as a 30B , 32A, and a 34AA. A 36C has the same cup size as a 28F.....

Bottom line: you can't discuss cup size without band size.


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What Guys Said 31

  • A tad confusing lol.

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  • I saw a post that said all girls are actually D. is this true?

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    • of course not.

  • I never new that. I definitely understood it.

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  • I understood it completely ! Lol is it weird? lol

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  • wow you girls are confusing when it comes to your bouncy parts , I know my Hannah says she is a 32B in some and a A in others for me she looks good in any of them hehe because she always gets herself re measured when getting new ones.

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  • i love small boobs

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  • Look at 32d, you can see her nipples lol

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  • Ahhhh this is so confusing :/

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  • Hahaha Thanks :)

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  • Hahahaha oh dear lord... mind=blown
    I was hoping this would make it a little easier but I'm confused now haha
    It was a good take, in depth but man its confusing how this all works haha

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  • I just care if they look good I don't care about these stupid numbers and letters

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    • I didn't ask?

    • I never claimed you did, I'm stating my opinion.

    • Wait are you the type of guy whod bitch about how a pair of boobs being shown to you looked? Wow and I thought people could not get more petty.

  • I was hoping to understand, but I am even more confused now. =( All I think I got is that the letters are the cups and the numbers are the band sizes. And the two combined indicate if a girls breasts are large or not.

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    • It means a woman can wear an A B C & so forth bra. They will just have different numbers for each of them.

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    • No, cup size is relevant to band size, don't feel like writing more.

    • Hmm true It isn't important

  • Mind = Blown

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  • I'm a guy and i seem to undestand this more than most women do 😂😂😂

    So I've said before that my "ideal" bra size on a woman is about 34C (when girls ask questions about preffered bra size for men). So if i understand this correctly: its the same as a 30DD, a 32D, a 36B, a 38A and so on...

    But i might want to reconsider my "ideal" bra size with that logic lol

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    • Eh. In my experience women know this.

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    • No. That's not what I said.
      I said (I'll repeat it for the second time) that the CUP sizes are the same. The amount of breast tissue a 32C carries is the same as a 34B and so forth. NO, someone who is a 32C can't wear a 34B as the BAND will be somewhat loose.

    • Oh i see. So the cup size is changeable, but the band size is not. So if she had a 32" band size, she could wear a 32A, 32B, 32C, and so on, depending on how bug her boob actually is.

      Well i guess that goes to show how much i know 😂

  • thats rocket science!

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  • Sounds like a silly system to me. Imagine if pants worked the same way. 30-32 and 34-32 were the 32 inch inseam isn't the same length.

    The way I see it, breasts takes a volume of space. Bra cups are supposed to ccontain said volume. Apply a range of specific volumes a cup size is supposed to handle and stick to it independently of band size.

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    • All A cups or B cups or C cups etc can't have the same volume, because they'll have to be further apart to accomdate the band size and such.

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    • Breasts change size, shape, and perkiness a lot so quite often! But I think we both agree something needs to change lol

    • haha Let's just say I wouldn't be a happy camper if my jeans size could be considered 30-30 at one place and 34-36 at another. I pretty much just grab and go. lol

  • A lot of errors here.

    First, band sizes go in 2” units while cup sizes go in 1” units, so going up one band size and down one cup size isn’t the same. Cup sizes are static increments. A 34B (34+2) means a 36” bust size. A 36A (36+1) means a 37” bust size. You’d need a 2 cup difference to yield the same bust measurement, e. g. a 32C (32+3) gives a 35” bust the same as a 34A (34+1) gives a 35” bust.

    But bust size doesn’t indicate cup *volume* since the bust measurement includes the underbust/band, it simply indicates the circumference of the entire bust. When you consider breasts large or small, they’re large relative to the chest they’re on. You need a ratio of cup size to band size to really illustrate it.

    So a 32C and a 34A both result in a 35” bust measurement. A C is 3” larger, so that means the bust is 9.3% larger than the band (3/32). Since the A is 1” larger, the bust is 2.9% larger than the band (1/34) even though the bust measurement winds up the same. You’re right that cup volume is dependant on band size, but wrong in how it works out.

    Also of note, because cup size is a static measurement, the same cup size gets a slightly larger ratio the smaller the band is. A 36C is 8.3% larger than the band, so the 32C gets an additional 1% (as I said, slightly). But as you can see, the ratio between a C cup on 2 different band sizes is much closer than the ratios when adjusting for bust size.

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    • I think you're misinterpreting what I'm saying.

      For one, I never said that band sizes DON'T go in 2" inincrements. In my examples I believe I made that obvious enough. And I think most people know that so I didn't bother to explicitly state it.

      Secondly, yeah... yes a 32C and a 34A would have the same bust measurement but relevant to band size a 32C would appear larger because someone who wears a 32C has a 32" underbust and someone with a 34A has a 34" under bust.
      I have to add though that this is all in theory. Because I am a 32B. And according to that method my underbust should be 32 and my overbust 34 but my underbust is 27" and over is 32". I've noticed that this method doesn't work for a lot of bra companies.

      Actually, no. Cups have volume. It isn't about your overbust measurement. Because the cup of a bra has depth to it, it is more about the volume of the cup and the overall size. If you compare the cup of a 34A to a 32B you will find they're exactly the same i same brand

    • I think you're just just throwing in information I've already stated in my own words, not really sure what you're arguing in your last point.

  • C's are average. It's the national, if not international average, no matter the number

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    • That's not true? a 36C is the national average in the US. in some countries its as high as a DD and low as an A. I'm pretty sure the second most common size is a 34B.

    • That's why I said national average if NOT the international one

    • well I'm also referring to the "no matter the number" part.

  • This makes sense to me. Reddit has a forum for this.

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  • Complicated confused 😕
    Though I've saved this method just in case if I happen to have the need to know the size of someone :p

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What Girls Said 22

  • THANK YOU! I have tried to explain this to some people on here and they just don't get it. Most people just assume they know a girls size only by the letter, but it really depends on the band size too. Like recently I said on here that I am a 32B, and I mentioned that it was small and some guy told me that it wasn't small because a B is bigger than an A. But a 32B is actually quite small and could be comparable to some A cups, again, depending on the band size.

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    • Haha yeah I'm tired of people saying "well B cups aren't small" like well not all B cups are the same size

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    • @LyricDollie Exactly. A lot of people don't know how it works. Lol

    • Right? I just gave up trying to explain it at a point. I typically just stick to one brand which is Victoria's Secret. It's a pain in the ass to try and get bras elsewhere. Each company does their sizing differently. And even though they said I was a 34B honestly the "sister size" according to them is the 32C which fits me better. The 34" bandwidth is too loose on me.

  • I'm even more confused. Which is the first and which is the second method?

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  • I just have them measure me at the store so I know which size I am to fit their particular line of bra.

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  • Ummm.. I'm even more confused now 😧

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  • This so badly needed to be written lol

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  • i am horribly confused...
    could you tell me what size i am? my measurements are 28'' and 36'' around the fullest part.
    if it helps, my current bra size in most brands is 34D, but it fluctuates quite often

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    • According to the method you're a 28H, or a 32D according to the second.

      How well does a 34D fit?

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    • *suggest

    • yeah,.. i don't live in America!!! i guess i will have to hunt, really,.. or search online i guess!
      thank you!

  • All this did was confuse me more lol. I just go to Victoria's Secret and get the free bra size measurement they do = problem solved.

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    • They vanity size 😏

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    • lol, yeah I understand :)

    • i really should go work at victorias secret. i've always wanted to measure boobs for a living

  • This post has just made bras a foreign concept to me. No wonder I have such trouble finding one that fits...

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  • So it's basically useless if I measure myself at home because it all depends on the store?
    I really hate having to shop for new bras >.<

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    • Honestly, pretty much. I'm sure you can get a good idea but who knows. The best thing to do is go try on bunch of different sizes.

  • I'm 32D and most people think I'm C.

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    • I think you have boobs. I don't care about numbers or letters.

    • @humbleteddy no one asked you what you think of her boobs

  • this totally makes sense to me. I have had a hard time finding the right bra size because in some brands I am a B while in other brands I am an A. I also usually do not only buy from just one bra brand either because bras can be extremely pricey, way more expensive than panties.

    When I was younger I kind of fell for that "bigger is better" thing so I never wanted to have small boobs. I always would like to try to find B bras that fit me because it made me think that my boobs were actually really bigger than they were since I use to think that the letter meant the actual size of the whole boob. So If i could fit a B cup then I was aloud to feel better about myself. It really sucks how the media and what not makes young girls feel bad about their bodies by telling them that they are not beautiful if they have small boobs. As I got older and became a woman I realized that many men find me and my small boobs attractive.

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  • what. i'm 34 D and my boobs ain't that small what the hell

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    • I don't recall saying that D cups are small?

      I don't think you even read the take

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    • @humbleteddy jesus. You're desperate. Blocked.

    • @Take Owner - Hahahaha

  • That's the most confusing thing I've ever read.

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  • Like I was a 32G and I fit nicely into a 34DDD. Nobody believes me when I tell them what size I am lol.

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  • you're right for the most part but b's will never be bigger than dd's because companies don't make band sizes that HUGE

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    • That's true, but its possible

  • I'm a bit confused about this. So if my under bust measurement is 40 & my cup measurement is 48, what size would I wear?

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    • It would depend on the bra manufacturer, at least in the US, since anything above DD doesn't have consistent sizing methods.

    • I normally wear a 38DD.

    • According to the method, 40H but I doubt that's accurate

  • Well then. I will admit I didn't know about the difference between cups while taking band sizes into consideration. I'm extremely confused though, my band width is 34" and my bust is 44", therefore I would be a 34J? But I usually wear 36DDDD and that feels comfortable. I just wish people would use the same measurements for everything lol

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    • Anything over DD has inconsistent sizing between brands. Best not to worry about generalities and be professionally fitted by a salesperson familiar with the brand you're interested in.

  • Yes this totally makes sense in some bras I'm a high B and mid C. It depends you don't know your true size until you get it professionally measured.

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  • That makes no sense. I wear a 34 DD and that method doesn't work for me.

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    • It doesn't work for me either, as I demonstrated. It doesn't "work" because not all companies make bras the same way. It does make sense tho.

    • for some brands though you'll find that it DOES work

  • I guess it makes sense. I wear a 36FF /: and it doesn't look THAT big!

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