Most women wear a band too large and cup too small. Bands stretch over time, so your "comfortable" 36C may actually be a stretched-out 34D. Our calculator sizes based on your current measurements, not habit. Try the recommended size and one sister size — you may be surprised.

Sister sizes keep the same cup volume while changing the band. Going down a band means going up a cup: 36C → 34D → 32DD all hold the same volume. This lets you fine-tune tightness vs. comfort without losing fit.

There is no universal standard for bra sizing. A 34D from Victoria's Secret, Panache, and Triumph can all fit differently because each brand uses its own patterns, fabrics, and cup shapes. Use our Brand Fit Guide to see your size converted per brand, and always try the nearest sister size when trying a new brand. Read the full guide →

Every 6-12 months, or after any significant body change — weight loss/gain, pregnancy, hormonal shifts, or starting a new fitness routine. Your band and cup can both change. Most women go through 6+ size changes in their lifetime.

Measure in a non-padded, unlined bra or a thin fitted top. Padded bras add volume to bust measurements, and thick layers add inches to the band. Both throw off the calculation — sometimes by a full cup size or more.

Tape-measure calculators become less precise above a G cup because breast tissue distribution, density, and shape have more impact at larger volumes. Our calculator gives a strong starting point, but for G+ sizes we recommend also using our Fit Fix checklist and trying 2-3 sister sizes. A professional fitting can also help for specialty sizing.