Find Your Estimated Bra Size
Enter your measurements for a quick starting size. For best accuracy, measure while braless or in a non-padded bra.
How this bra fitting calculator works
This bra size calculator estimates your starting size using two core values: your underbust measurement (to estimate band size) and your bust measurement (to estimate cup volume). If you include leaning and lying bust, the tool averages those with standing bust for a more balanced cup estimate.
Like every bra size chart, this calculator is a starting point, not a final verdict. Different brands, cup shapes, and fabric stretch can all influence your best fit. Think of the result as your baseline size for shopping and fitting.
Step-by-step measuring guide
1) Measure your underbust
Wrap a soft tape measure around your ribcage, directly under your bust. Keep it level and snug (firm but not painful). Exhale naturally before reading the number.
2) Measure your standing bust
Measure around the fullest part of your bust while standing upright. Keep the tape level and avoid compressing breast tissue.
3) Optional: leaning and lying bust
These extra measurements capture tissue distribution and can improve cup estimation, especially if your breast shape changes significantly with movement or posture.
Understanding band size and cup size
A bra size has two parts, such as 34D:
- Band size (34): based on ribcage/underbust measurement.
- Cup size (D): based on the difference between bust and band measurements.
Cup size is relative to band size. A 32D is not the same volume as a 38D. This is why sister sizing matters.
Sister sizes: useful when a bra almost fits
If the cup feels good but the band is too tight, go up one band size and down one cup letter. If the cup feels good but the band is too loose, go down one band size and up one cup letter.
- Example: 34D sister sizes are 32DD and 36C.
- Use sister sizes when a specific model runs tight or loose in the band.
Common bra fit issues and quick fixes
Band rides up in back
Usually means the band is too loose. Try a smaller band size (and adjust cup accordingly).
Straps digging in
Often caused by poor band support. Tight straps are usually a symptom, not the root cause. Check band size and cup volume first.
Cup spillage or quad-boob
Try a larger cup size. If band also feels tight, consider both a larger cup and sister size adjustment.
Gapping cups
Could mean cup is too large, but could also be a shape mismatch (for example, cup too tall for your breast root). Try another style before ruling out the size.
Tips for better bra shopping results
- Start on the loosest hook in a new bra (for longevity as elastic relaxes over time).
- Re-measure every 6–12 months or after weight/hormonal changes.
- Compare multiple styles: plunge, balconette, full coverage, and wireless can fit very differently.
- Check return policies when buying online.
Final note
The best bra fitting calculator gives a solid estimate, but comfort, support, and shape match are what truly matter. Use your calculated size as a launch point, then fine-tune by feel. A great fit should feel secure, balanced, and easy to wear all day.