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