Accurate Bra Size Calculator
Use a soft measuring tape and enter your numbers below. For best results, measure without a padded bra and keep tape parallel to the floor.
This calculator gives a starting size. Brand cuts, cup shape, and fabric stretch can change your best fit.
How to get an accurate bra size at home
Finding the right bra size is less about guessing and more about good measurements. If you have ever worn a band that rides up or cups that gape, your size may be off by more than one step. The calculator above uses underbust and bust measurements to estimate a reliable starting point, then gives sister sizes for easier shopping.
What makes a bra size “accurate”?
An accurate size balances two things: support from the band and containment from the cups. The band should do most of the support work, while cups should fully hold breast tissue without spillage or wrinkling. A good fit usually feels secure on the loosest hook when new, with straps that do not need to be over-tightened.
- Band: firm, level, and comfortable around the ribcage.
- Cups: smooth and containing tissue without overflow.
- Center gore: sits close to the sternum (for most wired bras).
- Straps: supportive but not digging into shoulders.
Step-by-step measuring guide
1) Snug underbust
Wrap the tape directly under the bust where the band sits. Pull snug (not painfully tight). Keep the tape level all the way around your body.
2) Standing bust
Measure around the fullest part of your bust while standing naturally. Keep tape soft and flat, not compressing tissue.
3) Leaning bust (recommended)
Lean forward so your torso is roughly parallel to the floor. Measure again at the fullest point. This helps capture softer or more projected tissue.
4) Lying bust (optional)
Lie on your back and measure bust circumference once more. This can improve estimates when shape changes significantly by position.
How the calculator works
The tool converts your entries to inches (if needed), rounds your snug underbust to the nearest even band size, and estimates cup size by the difference between band and average bust. If you enter standing, leaning, and lying values, the average improves consistency.
| Bust - Band Difference (in) | Estimated Cup |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD / E |
| 6 | DDD / F |
| 7+ | G and above |
Common sizing mistakes
- Adding extra inches to the underbust automatically.
- Using a loose tape for band measurement.
- Judging fit only by cup letter (without band number).
- Ignoring breast shape differences across brands and styles.
- Assuming one exact size fits all bra models.
Understanding sister sizes
If your calculated size feels close but not perfect, sister sizing can help. Going down one band size means going up one cup letter; going up one band size means going down one cup letter. Example: if 34D feels loose in the band, try 32DD. If 34D feels too tight in the band, try 36C.
Fit-check checklist after you buy
- Band stays level from front to back.
- No major cup overflow at top or sides.
- No empty space or wrinkling in cups.
- Underwire (if present) surrounds breast tissue, not on it.
- You can wear it for hours without pain points.
Final notes for better accuracy
Body composition, cycle-related changes, pregnancy, breastfeeding, weight changes, and different brands all influence fit. Re-measure every few months and whenever comfort changes. The best bra size calculator is a strong starting point, then small fit adjustments make it truly personal and accurate.