Bustyresources Wiki

A woman compares two sister sizes to her correctly-fitting bra (right).[1]

Cup size comparison sister sizes

Sister sizes always have the same cup volume as each other.[2]

A sister size is a related bra size with the same cup volume of each other. One's sister size could, in theory, be used as a substitute for one's true size, but the bra wouldn't fit correctly.[3]


Breast volumes

This illustration compares breast volumes. Listed volumes are volume per breast.[4]

Sister sizes have the same cup volume as each other. The difference of band size simply changes the fit. The idea behind sister sizes: If you increase the band size, you need to decrease the cup size to maintain the same volume. If you decrease the band size, you will need to increase the cup size therefore.[5]

Typical stores suggest sister sizes to sell their limited inventory to the customer, as opposed to a bra that actually fits. This perpetuates the problem of most women wearing band sizes too large, with correspondingly wrong cup sizes.[3]

Sometimes, two adjacent sister sizes may both fit a woman, since the cup volume is the same, while the band size can be adjusted to a small degree by using the hook and eye fasteners in the bra clasp.[3] However, it is usually less comfortable and flattering.


Main article: Bra sizing by country

UK sister sizes[]

Sister sizes (UK sizing)
26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
26A 28AA
26B 28A 30AA
26C 28B 30A 32AA
26D 28C 30B 32A 34AA
26DD 28D 30C 32B 34A 36AA
26E 28DD 30D 32C 34B 36A 38AA
26F 28E 30DD 32D 34C 36B 38A 40AA
26FF 28F 30E 32DD 34D 36C 38B 40A 42AA
26G 28FF 30F 32E 34DD 36D 38C 40B 42A 44AA
26GG 28G 30FF 32F 34E 36DD 38D 40C 42B 44A 46AA
26H 28GG 30G 32FF 34F 36E 38DD 40D 42C 44B 46A 48AA
26HH 28H 30GG 32G 34FF 36F 38E 40DD 42D 44C 46B 48A 50AA
26J 28HH 30H 32GG 34G 36FF 38F 40E 42DD 44D 46C 48B 50A 52AA
26JJ 28J 30HH 32H 34GG 36G 38FF 40F 42E 44DD 46D 48C 50B 52A 54AA
26K 28JJ 30J 32HH 34H 36GG 38G 40FF 42F 44E 46DD 48D 50C 52B 54A
26KK 28K 30JJ 32J 34HH 36H 38GG 40G 42FF 44F 46E 48DD 50D 52C 54B
26L 28KK 30K 32JJ 34J 36HH 38H 40GG 42G 44FF 46F 48E 50DD 52D 54C
26LL 28L 30KK 32K 34JJ 36J 38HH 40H 42GG 44G 46FF 48F 50E 52DD 54D
26M 28LL 30L 32KK 34K 36JJ 38J 40HH 42H 44GG 46G 48FF 50F 52E 54DD
26MM 28M 30LL 32L 34KK 36K 38JJ 40J 42HH 44H 46GG 48G 50FF 52F 54E
26N 28MM 30M 32LL 34L 36KK 38K 40JJ 42J 44HH 46H 48GG 50G 52FF 54F
28N 30MM 32M 34LL 36L 38KK 40K 42JJ 44J 46HH 48H 50GG 52G 54FF
30N 32MM 34M 36LL 38L 40KK 42K 44JJ 46J 48HH 50H 52GG 54G
32N 34MM 36M 38LL 40L 42KK 44K 46JJ 48J 50HH 52H 54GG
34N 36MM 38M 40LL 42L 44KK 46K 48JJ 50J 52HH 54H
36N 38MM 40M 42LL 44L 46KK 48K 50JJ 52J 54HH
38N 40MM 42M 44LL 46L 48KK 50K 52JJ 54J
40N 42MM 44M 46LL 48L 50KK 52K 54JJ
42N 44MM 46M 48LL 50L 52KK 54K
44N 46MM 48M 50LL 52L 54KK
46N 48MM 50M 52LL 54L
48N 50MM 52M 54LL
50N 52MM 54M
52N 54MM

US sister sizes[]

Sister sizes (US sizing)
28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58
28A 30AA
28B 30A 32AA
28C 30B 32A 34AA
28D 30C 32B 34A 36AA
28DD/E 30D 32C 34B 36A 37AA
28DDD/F 30DD/E 32D 34C 36B 38A 40AA
28DDDD/G 30DDD/F 32DD/E 34D 36C 38B 40A 42AA
28H 30DDDD/G 32DDD/F 34DD/E 36D 38C 40B 42A 44AA
28I 30H 32DDDD/G 34DDD/F 36DD/E 38D 40C 42B 44A 46AA
28J 30I 32H 34DDDD/G 36DDD/F 38DD/E 40D 42C 44B 46A 48AA
28K 30J 32I 34H 36DDDD/G 38DDD/F 40DD/E 42D 44C 46B 48A 50AA
28L 30K 32J 34I 36H 38DDDD/G 40DDD/F 42DD/E 44D 46C 48B 50A 52AA
28M 30L 32K 34J 36I 38H 40DDDD/G 42DDD/F 44DD/E 46D 48C 50B 52A 54AA
28N 30M 32L 34K 36J 38I 40H 42DDDD/G 44DDD/F 46DD/E 48D 50C 52B 54A 56AA
30N 32M 34L 36K 38J 40I 42H 44DDDD/G 46DDD/F 48DD/E 50D 52C 54B 56A 58AA
32N 34M 36L 38K 40J 42I 44H 46DDDD/G 48DDD/F 50DD/E 52D 54C 56B 58A
34N 36M 38L 40K 42J 44I 46H 48DDDD/G 50DDD/F 52DD/E 54D 56C 58B
36N 38M 40L 42K 44J 46I 48H 50DDDD/G 52DDD/F 54DD/E 56D 58C
38N 40M 42L 44K 46J 48I 50H 52DDDD/G 54DDD/F 56DD/E 58D
40N 42M 44L 46K 48J 50I 52H 54DDDD/G 56DDD/F 58DD/F
42N 44M 46L 48K 50J 52I 54H 56DDDD/G 58DDD/F
44N 46M 48L 50K 52J 54I 56H 58DDDD/G
46N 48M 50L 52K 54J 56I 58H
48N 50M 52L 54K 56J 58I
50N 52M 54L 56K 58J
52N 54M 56L 58K
54N 56M 58L
56N 58M


For people whose ideal bra size is somewhat of an outlier, like 28C or 36L, using a sister size (often a larger band/smaller cup) can allow the person to wear a particular bra that is otherwise off-limits to them due to being outsized. For example, someone who needs a 28C can try 30Bs to expand their selection of bra styles. They could then alter the band or use a Rixie Clip to make the bra fit better.

Some brands, or particular styles from some brands, can run smaller or larger than another bra of the same size. Because of this, someone who wears a size right outside the bra's size range could end up fitting into it because the bra band might run a little small or the cup might run big and vice versa.

Sister Sizes BFC

These bras all hold the same volume, but their proportions are very different.[6]


It is not recommended to wear a bra any more than one sister size away from your ideal bra size.[7][8] This is because, while, for example, sister sizes 34FF, 36F, 38E, 40DD, and 42D all hold the same volume, the bras are designed for very different body shapes. The higher in band/lower in cup you go, the shallower and wider the cup becomes. If the bra band is altered to be smaller, the way the cup fits will change and the straps also start out further.[9] The lower in band/higher in cup you go, the more projected and narrow the cups get. The more extenders used, the further out the straps lay, which can cause them to constantly slide off your shoulders as they now sit closer to the arms rather than the shoulder blade.


See also[]


External Links[]