Bust & Bra Size Estimator
Enter your underbust and full bust measurements to get an estimated band and cup size. This is a practical starting point for fitting, not a final verdict.
How this bust calculator works
A bust calculator compares two measurements: your underbust (around the ribcage, just beneath the breasts) and your full bust (around the fullest part). From there, it estimates a band size and a cup letter.
The core idea is simple:
- Band size is based mainly on your underbust measurement.
- Cup size is based on the difference between full bust and band size.
This model is widely used for quick sizing, especially in online shopping. It is useful, but still a starting point because brands, bra styles, and individual anatomy can change how a size feels.
How to measure correctly
1) Snug underbust
Wrap a soft measuring tape firmly around your ribcage directly under your bust. Keep the tape level all the way around and exhale naturally before taking the number.
2) Full bust
Measure around the fullest part of your bust with the tape parallel to the floor. Keep it gently snug, not tight enough to compress tissue.
3) Repeat once
Measure each point twice and use the average if your numbers vary. Consistent measuring technique produces better calculator results.
Understanding your result
Your result will include an estimated size such as 34C or 32DD/E. Here is what that means:
- Band number (e.g., 34) reflects ribcage fit and support.
- Cup letter (e.g., C) reflects bust volume relative to that band.
Cup letters are not absolute volume by themselves. A 32D and 36D do not hold the same volume because cup volume scales with band size.
Why fit can still vary
Brand differences
Different manufacturers grade cup shapes and wire widths differently. Two bras with the same printed size may fit very differently.
Style differences
Balconette, plunge, T-shirt, sports, and wireless designs all distribute support differently. One style may need a sister size even when another style in the same label fits perfectly.
Body variation is normal
Natural asymmetry, breast root width, projection, and tissue distribution can all affect fit. This is normal and expected.
Quick fit checklist after calculating
- The band should feel firm and level around your torso.
- Straps should support lightly, not carry most of the weight.
- Cups should contain tissue without gaping or cutting in.
- The center gore (if present) should sit close to the chest wall.
- You should be able to move, breathe, and lift arms comfortably.
When to recalculate
Recalculate your bust size every few months, especially if you've had changes in weight, training volume, hormonal cycle patterns, pregnancy/postpartum status, or if your current bras feel uncomfortable.
Final note
A bust calculator helps you start smarter and shop faster. Use the estimate as your baseline, then adjust based on comfort, support, and style goals. The best size is the one that fits your body today—not the one on an old label.