Cup Size Calculator
Enter your measurements to get a quick estimated bra size (band + cup). This is a starting point, not a perfect final fit.
How to calculate cup size
Cup size is usually estimated from the difference between your full bust measurement and your underbust measurement. Each inch (or about 2.5 cm) of difference generally moves you up one cup letter.
Most people need small adjustments after trying on real bras, because bra models, fabrics, and brands all fit a little differently.
The simple formula
- Band size: Round your underbust to the nearest even number (in inches).
- Cup step: Full bust minus underbust (in inches).
- Cup letter: Match the difference to a cup label (A, B, C, D, etc.).
Cup difference chart (approximate)
- Less than 0.5" difference: AA
- About 1": A
- About 2": B
- About 3": C
- About 4": D
- About 5": DD/E
- About 6": DDD/F
- About 7": G
- About 8": H
Example
If your underbust is 31.5" and your bust is 35":
- Band estimate: 32
- Difference: 35 - 31.5 = 3.5"
- Cup estimate: around C to D
That means a good starting range might be 32C or 32D, depending on bra style.
Why your measured size can still feel wrong
1) Brand variation
A 34C in one brand can fit more like a 32D or 34B in another. Manufacturing patterns are not identical.
2) Cup shape mismatch
Even with the right volume, cup shape can be too shallow, too projected, too tall, or too narrow for your body.
3) Strap and band tension
The band should do most of the support. If straps carry too much weight, your size may be off.
Fit checklist after calculating
- Band sits level and feels snug on the loosest hook.
- Center gore (middle panel) lies flat against the chest.
- No major cup gaping or overflow.
- Straps are secure but not digging into shoulders.
Bottom line
Use this calculator to get a reliable starting estimate. Then try nearby sizes (often called “sister sizes”) for the best comfort and support. A well-fitted bra should feel stable, smooth, and easy to wear all day.