Bra fit guide

The often-quoted claim that most women wear the wrong bra size comes from real studies. Here is what they found and how fitters check a bra.

What the research found

Study	Women	Finding
Clinical study, Journal of Science and Medicine in Sport, 2010	104, mean age 43.5	85% were wearing a bra that did not fit. Sizes chosen by the women, or by bra-sizing measurement systems, differed significantly from the size found by professional fitting criteria. Trying on several bras did not make self-selection more accurate.
Haworth et al., International Journal of Fashion Design, Technology and Education, 2025	24	Every participant failed the objective fit assessment, with 77 fit issues in total. The most common were cups too large, a front band that did not touch the sternum, and loose straps. The women's own reports matched the assessment in only 51% of cases.

The second study is the more useful one for shoppers. People are poor judges of their own fit, so a checklist works better than a feeling of comfort.

The band

It should sit level all the way around and not ride up your back.
One finger should fit under the front band: snug, not tight.
The centre front (the gore) should touch your breastbone. A gore that does not was one of the most common faults in the 2025 study.
Buy a new bra fastened on the loosest hook. As the elastic stretches you can move to the tighter hooks; if a bra only fits on the last hook it has worn out.

The cups

Wrinkles or empty space in the cup usually mean the cup is too large.
Tissue bulging over the top or sides means the cup is too small.
An underwire that pokes, or sits on breast tissue rather than lying flat against the chest, usually means the cup is too small.

The straps

Straps that slip off the shoulders, or dig in, point to a wrong band or cup size rather than a strap problem.

Why sizes are hard to compare

A bra size such as 34C has two parts: the band, measured around the ribcage under the bust, and the cup letter, which describes volume. The cup letter is relative to the band: a D cup on a 38 band holds more than a D cup on a 34 band. That is why "sister sizes" exist. Going one band size up and one cup letter down, for example from 34C to 36B, keeps roughly the same cup volume.

There is no single international system. Countries using the EN 13402 standard round the band to the nearest 5 cm, and brands also differ from each other, so the size on your last bra is a starting point, not an answer.

How often to get fitted

Breast size changes with weight, hormones, pregnancy and exercise. Fitters quoted by the Toledo Blade suggest a fitting at least every six months, and in 2010 a Council spokeswoman told HelloBeautiful that not getting fitted at all was the biggest mistake shoppers made.