US Bra Size Calculator
Use your underbust and bust measurements to estimate your US bra size. This calculator supports inches and centimeters.
- Underbust: Measure snugly around your ribcage, just under the breasts.
- Bust: Measure around the fullest part of the bust while standing naturally.
- Keep the tape level and parallel to the floor for both measurements.
How US Bra Sizing Works
US bra sizes combine a band size (the number) and a cup size (the letter). For example, in 34C, the band is 34 and the cup is C. The band is based on ribcage/underbust measurement, and the cup letter is based on the difference between bust and band.
A common misconception is that a cup letter means the same volume in every size. It does not. A 32D and 38D are very different in overall cup volume because the band size changes the cup scale too.
Quick Cup Difference Chart (US)
| Bust - Band Difference (in) | US Cup |
|---|---|
| < 1 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD/E |
| 6 | DDD/F |
| 7 | G |
| 8 | H |
| 9 | I |
| 10 | J |
| 11 | K |
Step-by-Step Measuring Guide
1) Underbust (Band)
Stand straight and exhale gently. Wrap a soft measuring tape around your ribcage directly under your bust. Keep it snug but not painfully tight. This is your underbust number.
2) Bust (Fullest Point)
Measure around the fullest part of the breasts, making sure the tape sits level all the way around your back. Don’t compress breast tissue. This is your bust number.
3) Use Consistent Units
If you measure in centimeters, keep both measurements in centimeters. The calculator converts to inches internally for standard US sizing.
Modern vs. Traditional (+4) Methods
Many fitters now prefer a modern approach where the band is close to your ribcage measurement, rounded to the nearest even number (e.g., 31.4 becomes 32). The traditional method adds 4 or 5 inches to underbust and can produce a looser band.
- Modern: Better starting point for supportive, contemporary fits.
- Traditional +4/+5: Useful if you prefer a more relaxed band feel or legacy brand charts.
What to Do After You Get a Size
Your calculated size is a starting estimate. Try the bra on and check fit points:
- Band should sit level and feel snug on the loosest hook.
- Center gore (middle panel) should lie close to your sternum in most underwire bras.
- Straps should not carry all the weight or dig painfully.
- Cups should contain tissue without gaping or spilling.
Sister Sizes Matter
If your band feels too tight but cups fit, go up one band and down one cup (example: 34D → 36C). If the band feels too loose, go down one band and up one cup (34D → 32DD).
Common Fit Issues and Fixes
- Spillage over cup edge: Try a larger cup (or different cup shape).
- Cup wrinkles/gaping: Try a smaller cup or a different style (balcony, plunge, full coverage).
- Band rides up in back: Usually band too large.
- Straps slipping: Tighten straps, test smaller band, or look for closer-set strap styles.
Frequently Asked Questions
How often should I remeasure?
Every 6-12 months, or sooner after body changes, pregnancy, significant weight change, or switching bra styles.
Is one size enough for all bras?
No. Different brands and styles vary. You may wear nearby sizes depending on fabric stretch and cup shape.
Can this calculator replace a professional fitting?
It’s a practical starting point, not a full replacement. A professional fitting can help with breast shape, asymmetry, and brand-specific sizing differences.
Note: This tool provides estimates for US bra sizing conventions and is for informational use.