Situations when a bra selected according to all the rules and calculations does not fit perfectly are not uncommon. The reasons may vary — from a slight measuring error to the individual shape of the breasts or the cup construction.
In such cases, it is important not to get discouraged and not to give up on comfortable lingerie. That is exactly why the concept of sister sizes (interchangeable sizes) exists.
Sister sizes are alternative bra sizes that have the same cup volume but a different underbust band measurement.
What Are Sister Sizes?
The principle is very simple: if the underbust measurement decreases, the cup size increases, and vice versa. Thanks to this, a bra can fit your body better, providing proper support and comfort.
For example, if a 75B bra feels slightly tight or does not fit perfectly, you may want to try 70C or 80A.
When Should You Consider a Sister Size?
- The bra feels tight under the bust, but the cup fits well
- The band feels comfortable, but the breasts “spill out” of the cups
- A model from another brand fits differently in the same size
- Your breasts have changed during pregnancy or breastfeeding
Sister Size Chart
The table below shows the most common interchangeable bra sizes.
| Main Size | Sister Sizes |
|---|---|
| 75A | 70B |
| 80A | 75B, 70C |
| 85A | 80B, 75C |
| 75B | 70C, 80A |
| 80B | 75C, 70D |
| 85B | 80C, 75D |
| 90B | 85C, 80D |
| 75C | 70D, 80B |
| 80C | 75D, 85B |
| 85C | 80D, 90B |
| 75D | 70E, 80C |
| 80D | 75E, 85C |
| 85E | 80F, 90D |
Important Tips
- Always try on several sister sizes
- Pay attention not only to the numbers but also to the overall fit
- Different brands may have different patterns and sizing
- During pregnancy and breastfeeding, breast size can change very quickly
The right sister size means comfort, beautiful breast shape, and confidence every day.