Bra Size & Cup Sizing Calculator
Find your accurate bra band and cup size using the modern standard measurement method, complete with international conversions (US, UK, EU, BR) and sister size alternatives.
Wrap the tape snugly directly under the bust along the ribcage, keeping the tape level.
Measure around the fullest part of your chest (across the nipples) without pressing down.
• 80% of breast support comes from a well-fitted band, not from tightening the shoulder straps.
• The center gore (wires between the cups) should sit flat against your sternum without gaping.
Sister Sizes (Equivalent Cup Volumes)
Alternate sizes that maintain the identical cup volume with tighter or looser band circumferences.
How it works
1
Measure snug underbust circumference directly below the breasts around the ribcage.
2
Measure loose bust circumference across the fullest part of the chest.
3
View your recommended US, UK, and European bra size alongside equivalent sister size options.
Frequently asked questions
What are bra sister sizes?
Sister sizes are bra sizes that share the exact same cup volume despite having different band circumferences. For example, 32D, 34C, and 36B all have identical cup volumes.
How is cup size determined?
Cup letters correspond to the difference between your bust and band measurement: 1 inch = A cup, 2 inches = B cup, 3 inches = C cup, 4 inches = D cup, 5 inches = DD/E cup, 6 inches = DDD/F cup.
Is this tool free?
Yes. The site is supported by ads, so you never pay or need to create an account.
Does it work on mobile?
Yes. The page adapts to your screen and does not require installing any app.