Sports Bra Sizing Guide
Confluence Running Sizing Guide
Support starts with the right measurements.
Sports bras use several sizing systems. The goal is not to force them into one conversion—it is to understand which system a specific style uses and how it should fit while running.
Start with two measurements
1. Underbust / rib cage
Wrap a soft measuring tape around your torso directly under the bust. Keep the tape level and comfortably snug.
2. Full bust
Measure around the fullest part of the bust with the tape level and without compressing the tissue.
Use those measurements with the specific brand's size chart. Different manufacturers calculate band and cup sizing differently, so one brand's conversion formula should not be treated as universal.
How a running sports bra should fit
Alpha sizing vs. band/cup sizing
Alpha-sized bras can be convenient, but two athletes who both wear a Medium may have very different band-to-cup proportions. Band-and-cup sizing can provide a more specific starting point when a style offers it. Neither system guarantees fit by itself; construction, compression level and intended support all matter.
If you are between sizes
First identify what is causing the mismatch. If the band feels right but the front is too small, a larger cup or differently proportioned style may be better than simply sizing the entire bra up. If the band rides up or shifts excessively, the band may be too loose.
Product construction changes the answer, so use style-specific guidance whenever it is available.
Oiselle sports bras
Oiselle currently uses multiple sizing systems across its sports-bra lineup, including numeric sizing on many styles and band/cup sizing on selected products. See our Oiselle Size Guide for brand-specific guidance.
Find the right support—not just the right label.
Compare support level, construction and fit along with size when choosing a running bra.
Follow the Journey
