Bra Cup Size Comparison: Why 30A Holds Less Volume Than 32A

Bra sizing combines two measurements:

• Band size: Underbust circumference, rounded to an even number (30, 32, 34…).
• Cup size: Difference between overbust (fullest part) and underbust.

The Calculation

• 30A: Underbust ~30", overbust ~32" → difference = 2" → A cup.
• 32A: Underbust ~32", overbust ~33" → difference = 1" → A cup.

Cup volume scales with band size. A 30A cup holds ~200 mL; a 32A holds ~240 mL. However, the letter denotes the difference, not absolute volume. Sister sizes (same cup volume): 30A = 28B = 32AA.

Key Takeaway

"Which is larger?" depends on definition:

• Larger cup volume: 32A > 30A.
• Larger cup letter for a given band: 30A represents a larger breast-to-frame ratio than 32A.

Proper fit requires measuring both circumferences and trying sister sizes.