Sister sizes are bra sizes that have the same cup volume but different band sizes. Understanding this concept can be a game-changer when your usual size is unavailable or when you need a slightly different fit.
What Are Sister Sizes?
Sister sizes maintain the same cup volume by adjusting both the band and cup letter. When the band size goes up, the cup letter goes down, and vice versa.
Think of it like this: the cup volume stays the same, but it's redistributed across a different band size.
How Sister Sizes Work
The relationship between sister sizes follows a simple pattern:
- Smaller band + Larger cup letter = Same volume
- Larger band + Smaller cup letter = Same volume
Example: 34C Sister Sizes
If you wear a 34C, your sister sizes would be:
- 32D (smaller band, larger cup letter)
- 36B (larger band, smaller cup letter)
All three sizes (32D, 34C, 36B) have the same cup volume!
The Science Behind Sister Sizes
Cup size is not absolute - it's relative to the band size. A C cup on a 32 band is much smaller than a C cup on a 38 band.
Cup volume formula:
Cup Volume = Band Size + Cup Letter Increment
This is why a 32D has the same volume as a 34C - the cup gets smaller as the band gets smaller.
Sister Size Chart
Here's a comprehensive sister size chart:
| Smaller Band | Your Size | Larger Band |
|---|---|---|
| 30C | 32B | 34A |
| 32D | 34C | 36B |
| 34DD | 36D | 38C |
| 36DDD | 38DD | 40D |
| 38G | 40DDD | 42DD |
| 40H | 42G | 44DDD |
When to Use Sister Sizes
1. Stock Availability
Your usual size is sold out, but sister sizes might be available.
2. Fit Adjustments
- Band too loose? Try the smaller sister size
- Band too tight? Try the larger sister size
- Between sizes? Sister sizes give you more options
3. Brand Variations
Different brands fit differently. Sister sizes help you find the best fit across brands.
4. Body Changes
Weight fluctuations, hormonal changes, or aging can make sister sizes more comfortable.
How to Choose Between Sister Sizes
Go Down a Band Size (32D instead of 34C) When:
- The band rides up your back
- You can pull the band away from your body more than 2 inches
- The bra feels loose overall
- You're between band sizes and need more support
Go Up a Band Size (36B instead of 34C) When:
- The band feels too tight or restrictive
- The band leaves deep marks on your skin
- You can barely fasten the hooks
- You need more room in the ribcage area
Important Considerations
Band Fit Changes
While cup volume stays the same, the band fit will be different:
- Smaller bands provide more support but less room
- Larger bands are more comfortable but provide less support
Strap Position
Sister sizes can affect where the straps sit on your shoulders due to the different band circumference.
Overall Silhouette
The shape and projection may vary slightly between sister sizes, even with the same cup volume.
Sister Sizes by Cup Size
A-B Cups
Sister sizing works well for smaller cups, giving you flexibility in band fit.
C-D Cups
Sister sizes are very useful for finding the perfect balance of support and comfort.
DD+ Cups
Sister sizing is crucial for larger cups, as proper band support becomes more important.
Common Sister Size Mistakes
1. Assuming All Sister Sizes Fit the Same
They have the same volume but different distributions - always try them on.
2. Only Going in One Direction
If 34C is too loose in the band, try 32D. If 32D is too tight, don't just go back to 34C - try 36B instead.
3. Ignoring Brand Differences
Sister sizes work differently across brands. A 32D in one brand might fit like a 34C in another.
Sister Sizes in Different Countries
Sister size relationships remain consistent across sizing systems:
US/UK System:
- 34C = 32D = 36B
EU System:
- 75C = 70D = 80B
AU System:
- 14C = 12D = 16B
Shopping Tips Using Sister Sizes
- Know your sister sizes before shopping
- Try multiple options when available
- Consider the garment type - some styles work better in different sister sizes
- Check the return policy when ordering online
Conclusion
Sister sizes are a powerful tool for finding better bra fit and having more shopping options. Remember:
- Same cup volume, different band sizes
- Use them to fine-tune your fit
- Always try before you buy when possible
- Consider your support needs when choosing between sister sizes
Understanding sister sizes opens up more possibilities for finding comfortable, well-fitting bras that make you feel confident and supported!
