What are Sister Sizes?

Cup size is entirely dependent on band size. Sister sizes hold the same volume of cup (amount of boob, if you will), but may fit better or worse depending on your preferred band measurement. For every band size you go up, you should go down an equal number of cup sizes, and vice versa.

For the purposes of this guide/calculator, the term "sister size up" means to go up in band size and down in cup size (32G > 34FF) and the term "sister size down" means to go down in band size and up in cup size (32G > 30GG).

Below is a chart with several sister sizes. Each row is a family - all the sizes listed on that row (same color) are sister sizes and have the same cup volume. Note that the further away you go from your estimated bra size, the less likely it is that the bra will fit. This chart is written with the UK sizing method, since it is more consistent.

26 28 30 32 34 36 38 40 42 44 46
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
26HH 38H 30GG 32G 34FF 36F 38E 40DD 42D 44C 46B
26J 28HH 30H 32GG 34G 36FF 38F 40E 42DD 44D 46C
26JJ 28J 30HH 32H 34GG 36G 38FF 40F 42E 44DD 46D
26K 28JJ 30J 32HH 34H 36GG 38G 40FF 42F 44E 46DD
26KK 28K 30JJ 32J 34HH 36H 38GG 40G 42FF 44F 46E
28KK 30K 32JJ 34J 36HH 38H 40GG 42G 44FF 46F
30KK 32K 34JJ 36J 38HH 40H 42GG 44G 46FF
32KK 34K 36JJ 38J 40HH 42H 44GG 44G
34KK 36K 38JJ 40J 42HH 44H 46GG
36KK 38K 40JJ 42J 44HH 46H
38KK 40K 42JJ 44J 46HH
40KK 42K 44JJ 46J
42KK 44K 46JJ
44KK 46K