If you’ve found that finding your right bra size is a frustrating process, there are some sizing hacks that can make finding your perfect fit much easier. One of the most effective of these is the use of “Bra Sister Sizes”. You may be unaware that every bra size has several "Sister Sizes"- these are sizes which have an equivalent cup capacity, despite the letter of the cup size being different. Knowing your sister sizes can help you find your best fit when buying bras that run smaller or larger than normal.
It’s a common misconception that the larger the cup size, the larger the bra, no matter what the band size (i.e. a 32F is larger than a 36B, a 34C is larger than a 38A, etc). However, this is not the case. During the bra manufacturing process the same exact bra cup may be paired with different band lengths to create multiple bra sizes. For example, the same exact cup is used to make 38A, 36B, 34C, 32D, AND 32DD bras! The reason for this is that within each cup size (A, B, C, D, DD, etc), as the band size increases, the cup size also slightly increases even though the letter does not. For example, a 34B bra and 36B bra will not only have different lengths, but the capacity of the cups will also differ. Once you understand that there are equivalent “sister sizes” to your own bra size, it can help you solve any bra fitting issues you may have.
Bra Sister Size Size Comparison Chart:
Each row shares the same cup size and each column shares the same band size.
Sizes in black are sizes we make. Sizes in light gray are sizes we dont make.
| 30 BAND SIZES |
Sister Size DOWN | Current Bra Size | Sister size UP |
28B | 30A | 32AA |
28C | 30B | 32A |
28D | 30C | 32B |
28DD | 30D | 32C |
| 32 BAND SIZES |
Sister Size DOWN | Current Bra Size | Sister size UP |
30B | 32A | 34AA |
30C | 32B | 34A |
30D | 32C | 34B |
30DD | 32D | 34C |
30DDD | 32DD | 34D |
30F | 32DDD | 34DD |
| 34 BAND SIZES |
Sister Size DOWN | Current Bra Size | Sister size UP |
32B | 34A | 36AA |
32C | 34B | 36A |
32D | 34C | 36B |
32DD | 34D | 36C |
32DDD | 34DD | 36D |
32F | 34DDD | 36DD |
| 36 BAND SIZES |
Sister Size DOWN | Current Bra Size | Sister size UP |
34B | 36A | 38AA |
34C | 36B | 38A |
34D | 36C | 38B |
34DD | 36D | 38C |
34DDD | 36DD | 38D |
34F | 36DDD | 38DD |
| 38 BAND SIZES |
Sister Size DOWN | Current Bra Size | Sister size UP |
36B | 38A | 40AA |
36C | 38B | 40A |
36D | 38C | 40B |
36DD | 38D | 40C |
Three Common Fit Problems and How to Solve them Using Sister Sizes:
1) If your cup fits but you need a different band size.
If the cups of your bra fit well but the band is too big or too small, getting your best fit will require both the band size AND cup size to change. For example, if you are wearing a 34B bra and the band is tight but the cups fits well, instead of going up to a 36B which may result in the cups being too large, you should choose your equivalent sister size, 36A.
2) If your band fits but you need a different cup size.
If your band fits great but your cups are too big or too small, keep the band size the same and just adjust the cup size based on your needs. For example, if you are wearing a 34B bra that fits in the band but has cups that are too small, you should choose a 34C.
3) If both your band and cup don't fit.
If you have fit troubles with both the band AND the cup, the band will change but the cup size will likely stay the same. For example, if you are wearing a 34B that is too small in both the band and the cup, you should try a 36B because it would have a larger band and a larger cup. Most women would think they should get a 36C, however a 36C would be an increase of both 1 band size and 2 cup sizes. By knowing your correct bra size, as well as what your sister sizes are, you will be able to choose the best option to give you a perfect fit. You’ll also eliminate much of the frustration associated with bra shopping! For more sizing help, international size conversions, or to try our new mobile sizing app, please go to our Sizing Help page by clicking here.
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FAQs
How does sister sizing work? A “sister size” is a size that has the same cup volume, but a different band length, as another size. So if a bra is a size 32B, its sister size “up” would be 34A, and its sister size “down” would be 30C.
How well do Sister sizes work? ›
Sister sizes do work well, but it's worth remembering that there are limits to what you can achieve. Sister sizing one up or one down is fine, and you might even be able to push it to two. But beyond that, the proportions of the bra will have changed so much that the bra probably won't be a good fit.
What is the sister bra size chart? ›
They are the sizes directly left and right of your measured size in the chart. All this means is the bras can hold the same volume. In the chart, find your size, then look at the sizes directly to the left and right of your size to find your sister sizes.
Is 34B and 32C the same? ›
Larger the band size, the larger the cup. Therefore, the cup of 34B is the same as 32C or 36A. Knowing your sister size will help you in finding the right-sized bra for you.
What to do if you're in between cup sizes? ›
In between cup sizes? Go up or down a half-cup! Bra sizes that share a row are called sister sizes, meaning they share the same cup volume (though they have different cup letters). For example, the row with bra sizes 36C, 38B, and 40A all have the same cup volume, but have different band sizes.
How do I know my sister size? ›
This is one band size larger than your current band size and one cup size smaller than your current Cup. For example, if you wear a 34C, your Sister Size UP would be 36B.
What is the sister size for DDD? ›
What Are Sister Sizes? Sister sizes are groups of bra-size equivalents that are related by cup volume. For example, a 36F (DDD) cup belongs to the same family as a 38E, a 40D, and a 42C.
Is a 34DD the same as a 36D? ›
Cup size represents the volume of your bosom and is completely relative to your band size. For example, a 36D holds 710cc of breast tissue - the same as a 34DD, 32F and 30G. A 34B, on the other hand, holds 390cc of breast tissue – the same as a 32C, 30D, and 28DD.
Is DDD the same as F? ›
The difference is truly in the name… DD or DDD are the US standard; E and F are used more internationally. As our range continues with a G cup, for example, we'll call it just that, a “G.”
Do sister bra sizes fit the same? ›
What is a sister size? Sister sizes are bras with the same cup volume. So, in theory your sister size could be swapped for your true size and fit just as perfectly, while the band would fit a bit tighter or a bit looser than usual.
Sister Size Down
Similarly, if your cup size is 34C, your sister down will be 32D (one band size lower and one cup size bigger). Opt for a sister size up when the band of your actual size bra is tight or too small. On the other hand, go for a sister size down when your cup is too small.
Why do Sister sizes exist? ›
Bra sister sizes share a similar cup volume but a different band and cup letter size. A bra sister size maintains cup capacity while adjusting the tightness of the band, leading to a better fit in some instances. For example, if a bra is a 30B, its direct sister size up is 32A, while down is 28C.
Why do my breasts fall out of the bottom of my bra? ›
If your bra stands away from you, or your breasts slip out the bottom of the cups when you lift your arms above your head, this is another clear sign that you are not wearing the correct size bra. If this happens, it means that the underband is too loose against your ribcage.
What is the most popular breast size? ›
Your breasts are unique
The average bra size in the United States is 34DD. This figure can vary by country.
Why does my bra get tighter as the day goes on? ›
It could be down to hormonal changes
Throughout the day, you may find that they affect all manner of things. Often enough, an increase in hormones could mean that your breasts swell or start to feel larger. That is typically completely normal but it can play havoc with your lingerie.
Why do my breasts fall out of the top of my bra? ›
If it is inching upwards, it could mean that the band size is wrong. A smaller band and cup size will result in your breasts spilling out over the cups. Secondly, check the cup size. Cups that are too small will result in spillage, so try going up a cup size.
Is 36C the same as 34DD? ›
"The letter part of a bra size represents the difference between your back and bust measurements. For example, a 36C is the same cup size as a 34D and 32DD. This is because as the back size, or the number, gets smaller, the difference between your back and bust increases.
Is 36A the same as 34B? ›
Another example, a 34B and 36A are the same cup size. The only difference is the band size. The 36 is a bigger band size than the 34. Here's an example of some other sister sizes.
What is the difference between 36B and 36C? ›
3) If both your band and cup don't fit.
For example, if you are wearing a 34B that is too small in both the band and the cup, you should try a 36B because it would have a larger band and a larger cup. Most women would think they should get a 36C, however a 36C would be an increase of both 1 band size and 2 cup sizes.
Is 34B and 36A the same? ›
Another example, a 34B and 36A are the same cup size. The only difference is the band size. The 36 is a bigger band size than the 34. Here's an example of some other sister sizes.
Remember: if you go up a band size, you need to go down a cup size, and vice versa. (Ex: A 34C cup is the same as a 36B. A 40E(DD) cup is the same as a 42D.)
Is a 38B the same as a 36C? ›
For example, if you wear a 38B, your Sister Size Up would be 40A, and your Sister Size Down would be 36C. You can wear either one of the Sister Sizes and still have the same cup volume as 38B! The only difference is that you'd probably need to use the furthest or the tightest hook of the bra, instead of the middle one.
