Lifestyle 2026-05-04 3 min read By Konvertibly Team

Bra Size Calculator: Band Size, Cup Size, and Sister Sizes

Calculate bra size from band and bust measurements. Understand sister sizes, international bra sizing (US, UK, EU), and how to get the right fit.

How to Calculate Bra Size

Bra size has two parts: band size (around the ribcage) and cup size (difference between bust and band). Getting both right is essential for comfort and support.

Measurement Method

Step 1 — Band size:
Measure snugly under bust (cm or inches)
Round to nearest even number (or add 1 if odd)
US band sizes: 28, 30, 32, 34, 36, 38, 40...

Step 2 — Cup size:
Bust = measure at fullest point of chest
Difference = Bust - Band size (inches)
  0"  = AA  | 1" = A | 2" = B | 3" = C
  4"  = D   | 5" = DD/E | 6" = DDD/F

International Size Conversion

US 34B = UK 34B = EU 75B = FR/ES 90B
US 34D = UK 34D = EU 75D
Cup letters vary between US and EU:
US DD = UK DD = EU E
US DDD = UK E = EU F

Sister Sizes

Bands +2, cups −1 letter = same volume:
34C = 36B = 32D (all same cup volume)
If band too tight: try same cup, larger band
If band too loose: try same cup, smaller band

Calculate bra size: Free Bra Size Calculator