Sister Size Calculator
Every bra size has sisters: sizes that hold the same cup volume on a different band. Enter your size to see them instantly.
Enter your size
How it works: going down one band size while going up one cup keeps the cup volume the same. Going up a band while going down a cup does the same in reverse. The whole system in one picture (every size colored by volume, sister chains as diagonals) lives at the sister size web.
Sister sizes change the band length only. The breast volume the cup holds is identical across the whole sister-size row.
Every dome holds the same volume; only the band bar changes length. Tap a size to compare.
How sister sizes work
A cup letter only describes volume relative to its band. A 34C cup and a 36C cup are not the same size: the 36C is larger, because each cup letter adds one inch to a bigger frame.
Go down one band and up one cup (34C → 32D) and the cup volume stays constant while the band gets two inches snugger. Go up a band and down a cup (34C → 36B) for a looser band with the same cups.
Sister sizes solve one problem: cups fit, band doesn't. If the cups themselves gape or spill, you need a different cup size, not a sister size.
Sister size chart
Read across any row: every size on the row holds the same cup volume. Seventy-two US sizes, 28A to 44H, each with its sisters one and two bands away; tap a size for its guide.
| −2 bands | −1 band | Size | +1 band | +2 bands |
|---|---|---|---|---|
| — | — | 28A | 30AA | — |
| — | — | 28B | 30A | 32AA |
| — | — | 28C | 30B | 32A |
| — | — | 28D | 30C | 32B |
| — | — | 28DD | 30D | 32C |
| — | — | 28DDD | 30DD | 32D |
| — | — | 28G | 30DDD | 32DD |
| — | — | 28H | 30G | 32DDD |
| — | 28B | 30A | 32AA | — |
| — | 28C | 30B | 32A | 34AA |
| — | 28D | 30C | 32B | 34A |
| — | 28DD | 30D | 32C | 34B |
| — | 28DDD | 30DD | 32D | 34C |
| — | 28G | 30DDD | 32DD | 34D |
| — | 28H | 30G | 32DDD | 34DD |
| — | 28I | 30H | 32G | 34DDD |
| 28C | 30B | 32A | 34AA | — |
| 28D | 30C | 32B | 34A | 36AA |
| 28DD | 30D | 32C | 34B | 36A |
| 28DDD | 30DD | 32D | 34C | 36B |
| 28G | 30DDD | 32DD | 34D | 36C |
| 28H | 30G | 32DDD | 34DD | 36D |
| 28I | 30H | 32G | 34DDD | 36DD |
| 28J | 30I | 32H | 34G | 36DDD |
| 30C | 32B | 34A | 36AA | — |
| 30D | 32C | 34B | 36A | 38AA |
| 30DD | 32D | 34C | 36B | 38A |
| 30DDD | 32DD | 34D | 36C | 38B |
| 30G | 32DDD | 34DD | 36D | 38C |
| 30H | 32G | 34DDD | 36DD | 38D |
| 30I | 32H | 34G | 36DDD | 38DD |
| 30J | 32I | 34H | 36G | 38DDD |
| 32C | 34B | 36A | 38AA | — |
| 32D | 34C | 36B | 38A | 40AA |
| 32DD | 34D | 36C | 38B | 40A |
| 32DDD | 34DD | 36D | 38C | 40B |
| 32G | 34DDD | 36DD | 38D | 40C |
| 32H | 34G | 36DDD | 38DD | 40D |
| 32I | 34H | 36G | 38DDD | 40DD |
| 32J | 34I | 36H | 38G | 40DDD |
| 34C | 36B | 38A | 40AA | — |
| 34D | 36C | 38B | 40A | 42AA |
| 34DD | 36D | 38C | 40B | 42A |
| 34DDD | 36DD | 38D | 40C | 42B |
| 34G | 36DDD | 38DD | 40D | 42C |
| 34H | 36G | 38DDD | 40DD | 42D |
| 34I | 36H | 38G | 40DDD | 42DD |
| 34J | 36I | 38H | 40G | 42DDD |
| 36C | 38B | 40A | 42AA | — |
| 36D | 38C | 40B | 42A | 44AA |
| 36DD | 38D | 40C | 42B | 44A |
| 36DDD | 38DD | 40D | 42C | 44B |
| 36G | 38DDD | 40DD | 42D | 44C |
| 36H | 38G | 40DDD | 42DD | 44D |
| 36I | 38H | 40G | 42DDD | 44DD |
| 36J | 38I | 40H | 42G | 44DDD |
| 38C | 40B | 42A | 44AA | — |
| 38D | 40C | 42B | 44A | 46AA |
| 38DD | 40D | 42C | 44B | 46A |
| 38DDD | 40DD | 42D | 44C | 46B |
| 38G | 40DDD | 42DD | 44D | 46C |
| 38H | 40G | 42DDD | 44DD | 46D |
| 38I | 40H | 42G | 44DDD | 46DD |
| 38J | 40I | 42H | 44G | 46DDD |
| 40C | 42B | 44A | 46AA | — |
| 40D | 42C | 44B | 46A | 48AA |
| 40DD | 42D | 44C | 46B | 48A |
| 40DDD | 42DD | 44D | 46C | 48B |
| 40G | 42DDD | 44DD | 46D | 48C |
| 40H | 42G | 44DDD | 46DD | 48D |
| 40I | 42H | 44G | 46DDD | 48DD |
| 40J | 42I | 44H | 46G | 48DDD |
US cup progression: A · B · C · D · DD · DDD · G · H · I · J · K. One step in either direction is the useful range; two steps shows why a band four inches off never fitted. The equivalent chart adds the UK and EU labels for every row.
Sister sizes: answered
What is a sister size?
A sister size is a bra size with the same cup volume as yours but a different band length. 34C, 32D and 36B are sister sizes: the cups hold the same volume, only the band changes.
When should I try a sister size?
When the cups fit correctly but the band is wrong. Band rides up, feels loose, or you're on the tightest hook on day one: go down a band and up a cup. Band digs in or leaves marks: go up a band and down a cup.
Is a 34C the same as a 36B?
Same cup volume, different band. The 36B has a band two inches longer. Because the band provides most support, a 36B will feel looser and offer less lift than a 34C on the same body.
How many sister sizes does a bra size have?
In theory the whole row: every step of one band up and one cup down. In practice one step in either direction fits well; two steps changes the wire width and cup shape enough that fit usually suffers.
Do sister sizes work across brands?
The math is universal, but cut varies by brand. Sister sizes are the right starting point when a brand runs tight or loose in the band, then adjust for that brand's cup shape.
Opens HauteFlair’s own hub page; use your measured size there. HauteFlair is owned by the same company as Brasize.ai; that relationship never changes the sizing math, charts, or fit advice on this page. How this site makes money.
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