Bra sister sizes
Bra sister sizes keep a similar cup relationship as the band changes: move one band step larger and one cup letter smaller, or one step smaller and one letter larger.
Sister sizes of 34C
- Two bands down30DDUK 30DD
- One band down32DUK 32D
- Your size34CUK 34C
- One band up36BUK 36B
- Two bands up38AUK 38A
Each band step up (2 inches) takes the cup one letter down, and each band step down takes it one letter up.
Sizes are listed only where the tables hold both the band (28 to 60) and the cup (AA to O), so a size at the edge has fewer sisters.
A sister size follows the rule above, but brands cut bands and cups differently. Try on before you decide.
Sister size table for bands 30 to 40
Each cell shows the sister one band down, then the sister one band up, in US sizing.
| Band | A | B | C | D | DD/E |
|---|---|---|---|---|---|
| 30 | 28B / 32AA | 28C / 32A | 28D / 32B | 28DD / 32C | 28DDD / 32D |
| 32 | 30B / 34AA | 30C / 34A | 30D / 34B | 30DD / 34C | 30DDD / 34D |
| 34 | 32B / 36AA | 32C / 36A | 32D / 36B | 32DD / 36C | 32DDD / 36D |
| 36 | 34B / 38AA | 34C / 38A | 34D / 38B | 34DD / 38C | 34DDD / 38D |
| 38 | 36B / 40AA | 36C / 40A | 36D / 40B | 36DD / 40C | 36DDD / 40D |
| 40 | 38B / 42AA | 38C / 42A | 38D / 42B | 38DD / 42C | 38DDD / 42D |
A band step is 2 in. For example, 34C has 32D one step down and 36B one step up. Two steps down gives 30DD/E in US, while two steps up gives 38A in US.
Sister sizes are listed up to two steps in each direction, within the band chart from 28 to 60 and where a cup row exists for a difference of 0 to 15 in. Sizes at the chart ends have fewer listed sisters.
Some sizes have fewer options. The listed sister size for 28A is 30AA, one band step up and one cup letter down. For 34AA, the listed options are 32A, one step down and one letter up, and 30B, two steps down and two letters up. The 32A label is not listed in JP, and the two-step-up option for 34C is not listed in JP.
A sister size changes the band fit, so the fit differs from the size it comes from. Labels follow the usual rules: the band comes from the band chart, and cup letters come from the difference in each of the six systems. A calculated size is a starting point because methods, rounding and charts differ between published guides, and JP letters vary by brand. People measure again and try on.
Where next
Convert a size between systems, calculate one from measurements or read the full chart.
Sister size questions
What is a sister size?
A sister size moves the band one step and the cup one letter the other way. The sisters of a 34C are 32D (one band down) and 36B (one band up).
How many sister sizes does a size have?
This page shows two steps each way, up to four sisters. The tables list bands 28 to 60 and cups AA to O, so a size near either end has fewer.
Do sister sizes fit the same?
The rule only moves the band and the cup together on paper. How a bra fits depends on the brand and on you, so measure again and try on.