Sports Bra Size Calculator
Find your band and cup size from underbust and bust measurements, plus the support level suited to your workout’s impact.
Your sports bra size
Recommended support: High/maximum support (running, HIIT, plyometrics, court sports)
Band size uses the traditional underbust-plus-allowance method; cup size is the difference between bust and band, each inch stepping up one cup letter. Sizing varies by brand — treat this as a fitting-room starting point.
Why band and support level both matter
A sports bra that fits at rest can still fail during a workout if it isn’t matched to the right support category. The band does most of the actual work — it should sit snug and level all the way around, not just at the front — while the cup should fully contain without gaping or spilling. Getting the band right first, then the cup, then the support level for your activity is the order that produces the fewest surprises once you're moving.
Support level is really about how the bra is built: compression styles flatten against the chest, encapsulation styles shape and support each side individually, and combination designs do both — the usual choice for higher-impact training.
Frequently Asked Questions
How is sports bra size calculated?
Band size comes from your underbust measurement (snug, directly under the bust): round it to the nearest whole inch, then add 4 if that number is even or 5 if it's odd — the traditional sister-size fitting method, which always lands on an even band number. Cup size is the difference between your bust measurement and that band size, with each inch of difference stepping up one cup letter from AA.
Why do I need a different support level for different workouts?
Breast tissue moves in multiple directions during exercise, and how much it moves scales with impact. Low-impact activity like yoga or strength training needs comfort and coverage more than compression; high-impact activity like running or HIIT involves the most vertical and side-to-side motion, so it calls for maximum encapsulation or combination (encapsulation + compression) support to actually limit that movement.
My band and cup came out different from the bra I currently wear. Why?
Sizing isn't standardized across brands — a 34C in one brand can fit like a 32D or 36B in another, especially between everyday bras and sports bras, which are often built with less stretch in the band. Treat the calculated size as a fitting-room starting point and try the neighboring sister sizes if the first one feels off.
Should I size up or down for a tighter sports bra fit?
For high-impact workouts, many people size down one band (for a firmer, more stable fit) while keeping the same cup, or move to a specific high-support style rather than just changing the number. If a size feels restrictive around the ribs or digs in at the shoulders, that's a sign to size up the band rather than loosen the straps.
How often should I re-measure?
Body composition, weight changes, and even the menstrual cycle can shift measurements by an inch or more. It's worth re-measuring every six months to a year, or any time a bra that used to fit well starts riding up at the band or spilling at the cup.
This tool is not professional fitting or medical/fitness advice — it's a general estimate to narrow your search. For a precise fit, a professional bra fitting is worth the twenty minutes.