Women's Fashion

Bra Sister Size Calculator: Find Your Sister Sizes

Free tool · Updated October 2, 2026 · By CouponTalk

Your result

Enter your measurements to see your result.

Quick answer

Sister sizes share the same cup volume on a different band. Go one band size up and one cup size down, or one band down and one cup up: 34B, 36A and 32C are all sister sizes. Use a sister size when the cups fit but the band feels too tight or too loose.

How to measure

Select your current band and cup size.
If the band is too tight, move one size right (bigger band, smaller cup).
If the band rides up, move one size left (smaller band, bigger cup).

Bra Sister Size Chart

Bra sister sizes: each row has the same cup volume
30 band	32 band	34 band	36 band	38 band
30D	32C	34B	36A	38AA
30DD	32D	34C	36B	38A
30E	32DD	34D	36C	38B
30F	32E	34DD	36D	38C

Sizes vary between brands by 1–2 cm. Always check the brand's own size chart before you buy.

Frequently asked questions

What is the sister size of 34B?

The sister sizes of 34B are 32C (smaller band) and 36A (bigger band). All three have the same cup volume.

When should I wear a sister size?

When the cups fit well but the band is uncomfortable. A band that digs in needs the sister size up; a band that rides up your back needs the sister size down.

Is 36B the same as 34C?

Yes, 36B and 34C are sister sizes with the same cup volume, but the band on 36B is about 2 inches looser.