What Are Sister Sizes
Sister sizes are bra sizes that have the same cup volume but different band sizes and cup letters. As band size increases by one size (e.g., 32 to 34), cup letter decreases by one (e.g., F to E) to maintain the same cup volume. As band size decreases, cup letter increases. This works because cup volume is determined by the difference between bust and band measurements — not by the cup letter alone. A 34F and a 36E and a 32G all have cups of the same volume, just on different band circumferences.
When to Use Sister Sizes
Band too tight, cup correct: go up one band size and down one cup letter (e.g., 34G → 36FF). The cup volume stays the same; the band is looser. Band too loose, cup correct: go down one band size and up one cup letter (e.g., 36E → 34F). The cup volume stays the same; the band is firmer. Between sizes: if you measure between even numbers for the band, your sister sizes are the two adjacent band sizes with adjusted cups — try both and choose the one that fits better in the band. Sister sizes are most useful as a temporary fix or when your exact size is unavailable; a bra in your true size will always fit better than a sister size.
Sister Size Chart (D+ Focus)
Key sister size groups for D+ cup wearers:
- 28HH / 30H / 32G / 34FF / 36F / 38E — all the same cup volume
- 28J / 30HH / 32H / 34G / 36FF / 38F — all the same cup volume
- 30K / 32J / 34HH / 36H / 38G / 40FF — all the same cup volume
- 32K / 34J / 36HH / 38H / 40G — all the same cup volume
In US sizing, the letters progress differently (no FF, GG etc.) — convert by checking brand-specific size guides, as US and UK cup letters diverge significantly above DD.
Chimera Costumes — Heidi Lange
Gothic cosplay creator and curvy content producer who documents wearing and building structured garments for her augmented, busty figure — making her content directly relevant to D+ cup wearers navigating the same challenges.