Find Your Estimated Bra Size
Use this tool as a reliable starting point for bra shopping. Enter your underbust and full bust measurements, then compare the result with how real bras fit your body.
How this right bra size calculator works
A bra size has two parts: band size (the number) and cup size (the letter). This calculator estimates both using a straightforward fit method:
- Band size comes from your snug underbust measurement, rounded to the nearest even number.
- Cup size comes from the difference between your full bust and calculated band size.
- The result is an estimated starting size to test in real bras.
No calculator can replace trying on bras, because fabrics, brand grading, cup shape, and strap construction vary widely. But this gets you close quickly and helps prevent blind guessing.
How to measure correctly at home
1) Underbust (snug)
Wrap a soft measuring tape around your ribcage directly under your bust. Keep the tape level all the way around. Exhale normally, then take the measurement snugly (not painfully tight).
2) Full bust
Measure around the fullest part of your bust while standing upright. Keep the tape horizontal, and make sure it is not digging in or hanging loose.
3) Repeat for consistency
Take each measurement 2–3 times and use the average if values vary. Even a half-inch can change cup recommendation in many size ranges.
Band and cup: what they really mean
A common confusion is assuming cup letters are absolute. They are not. Cup size is relative to band size. For example, a 34D and 38D have different cup volumes because the bands are different.
That is why your best fit may be a neighboring “sister size” if the band feels wrong but cup volume seems close.
| Bust - Band Difference (inches) | Approx Cup (US) | Approx Cup (UK) |
|---|---|---|
| 0 | AA | AA |
| 1 | A | A |
| 2 | B | B |
| 3 | C | C |
| 4 | D | D |
| 5 | DD/E | DD |
| 6 | DDD/F | E |
Quick fit check after you calculate
- Band: should feel secure on the loosest hook when new; it should not ride up your back.
- Center gore: should sit close to the sternum in most wired bras.
- Cups: no major spilling, cutting, or empty wrinkling.
- Straps: should support lightly, not carry all weight.
Sister sizes explained simply
If the cup volume feels right but the band is uncomfortable, try sister sizing:
- Band feels tight: go up one band and down one cup (example: 34D to 36C).
- Band feels loose: go down one band and up one cup (example: 34D to 32DD).
The calculator gives suggested sister sizes automatically when available.
Most common fit mistakes
Wearing a band that is too large
This is extremely common. A loose band shifts weight to straps, causing shoulder pressure and unstable support.
Choosing cups too small
If tissue spills over top or sides, increase cup volume first before assuming the band is wrong.
Using only one brand or one style
Different brands scale sizes differently, and different bra constructions fit different breast shapes. Try multiple styles before deciding your “true size” is wrong.
FAQ
Is this calculator accurate?
It is accurate as a starting framework. Final fit depends on brand, style, cup shape, and personal comfort preference.
Can my size change?
Yes. Hormonal changes, body composition shifts, pregnancy/postpartum changes, and aging can all affect bra fit. Re-measure periodically.
Should I measure in centimeters or inches?
Either is fine. This calculator supports both and converts automatically.
Final note
Use your calculated size to narrow your options, then confirm with a practical fit test. The best bra size is the one that gives stable support, comfort through the day, and a natural feel for your body.