Sister Bra Sizes: The Complete Guide

What Are Sister Bra Sizes?

Sister sizes are bra sizes that keep a similar cup volume while changing the band length. This helps when your base size feels tight or loose, or when your size is out of stock.

Core rule: down band → up cup; up band → down cup

Quick Examples

• 34C → sister sizes: 32D, 36B
• 32DD → sister sizes: 30E, 34D
• 36B → sister sizes: 34C, 38A

Across Different Systems

The concept stays the same across US/UK/EU/JP systems, but cup letters differ. It's best to find sister sizes within one system first, then convert between systems if needed.

How to Use Sister Sizes

1. Find your base size with our Bra Size Calculator.
2. If the band is tight, try one band up and one cup down. If it’s loose, try one band down and one cup up.
3. Use our Sister Sizes Finder to get instant suggestions.
4. When switching brands, try our Brand Size Converter and consider sister sizes.

Practical Tips

• Try 1–2 steps; more steps may change support and shape too much.
• Check brand-specific charts—sizing can vary between brands and styles.
• For EU/JP systems, band steps are 5 cm; US/UK bands step by 2 inches.
• Comfort and support matter most—use sister sizes to fine-tune fit.