Which Bra Is Right for You? Learn More
Bra sister sizes are different band-and-cup combinations with similar cup volume. They can help when the cups fit but the band needs adjusting. For example, the nearest sister sizes to 36C are 34D for a smaller band and 38B for a larger band.
The rule is simple: go up one band size and down one cup step, or down one band size and up one cup step. Sister sizing is a starting point for trying a different fit, not a promise that another size or brand will fit the same.
Bra Sister Size Chart
Find your current size in the middle column. The left column gives a smaller-band option; the right gives a larger-band option. Each row represents similar cup volume. These examples use conventional band-and-cup sizing, not SHEFIT size names.
| Smaller band | Current size | Larger band |
|---|---|---|
| 28C | 30B | 32A |
| 30D | 32C | 34B |
| 32D | 34C | 36B |
| 34D | 36C | 38B |
| 36D | 38C | 40B |
| 38D | 40C | 42B |
| 44D | 46C | 48B |
| 46D | 48C | 50B |
Check the brand's cup sequence before calculating beyond D. US and UK labels, including DD, DDD, E and F, are not interchangeable across every brand. Availability of a sister size also varies.
How to Calculate Your Sister Size
If the cups fit but the band is too tight
Try the next band size up and one cup step down. For example, 34C becomes 36B, and 36C becomes 38B. Moving from 36C to 38C increases cup volume as well as band size, so it is not the same adjustment.
If the cups fit but the band is too loose
Try the next band size down and one cup step up. For example, 36C becomes 34D. Recheck the entire fit: the band should stay level and secure, the cups should contain your bust, and the straps should feel comfortable.
If the cups do not fit
Sister sizing aims to keep cup volume similar. If you need more or less cup space, or both the band and cups feel wrong, measure again and consult that brand's chart instead of automatically choosing a sister size.
Why the Cup Letter Changes
A cup letter does not describe a fixed volume on its own. It works with the band size. A 30C and a 40C therefore have different cup volumes, while nearby combinations such as 38D, 40C and 42B have similar volume.
Similar volume does not guarantee identical fit. Cup shape, fabric, straps and the design of the bra can all change how it feels. Start with a neighboring size rather than making several band-size jumps to find an available option.
Does Sister Sizing Apply to SHEFIT Sports Bras?
For SHEFIT Ultimate, Flex and Emerge, use your bust and rib-cage measurements with the chart for the specific bra. These designs use SHEFIT size names, so a conventional size such as 36C is not a direct substitute for checking the chart.
Start with the SHEFIT fit guide and size charts. Then use the Ultimate, Flex and Emerge comparison to choose the construction and support you prefer. Adjustable straps and a rib band help you personalize the fit after choosing a size; they do not eliminate the need for appropriate cup coverage.
For more on how these features work together, read our guide to adjustable-strap sports bras.
Common Sister-Size Questions
What are the sister sizes for 40C?
38D has a smaller band and 42B has a larger band, with similar cup volume. Choose based on how the band fits, then check cup coverage and comfort.
What is the sister size for 46C?
The neighboring options are 44D and 48B. They change band fit while keeping cup volume similar; neither is guaranteed to feel identical to your current bra.
Are 32DDD and 32F always the same?
No. Letter conventions vary by brand and sizing system. Check that brand's conversion chart. A change in cup label with the same band number may be a naming conversion, not sister sizing.
Should I replace a worn-out bra with a sister size?
Not automatically. A stretched band or worn straps can change how your current bra feels. Take fresh measurements and assess a new bra's fit before deciding that you need a different size.
