Bra Size Calculator
Measure in inches while wearing a non-padded bra or no bra.
The two measurements
Bra size combines a band measurement and a cup measurement, and both are derived from measuring tape readings rather than guessed.
- Band — measured snugly around the ribcage directly beneath the bust, with the tape level all the way round.
- Bust — measured around the fullest part of the chest, with the tape relaxed rather than pulled tight.
How cup size is derived
Each inch of difference moves you up one cup letter.
| Difference | Cup (US) |
|---|---|
| 1" | A |
| 2" | B |
| 3" | C |
| 4" | D |
| 5" | DD / E |
| 6" | DDD / F |
Example: a 34" band with a 37" bust is a 3-inch difference, giving 34C.
Cup letters are not absolute
This is the part that surprises people. A cup letter only means something attached to its band number. A 32D and a 36D hold noticeably different volumes, because the cup scales with the band.
This is why sister sizes work: going down a band and up a cup keeps roughly the same volume. If a 34C band feels loose, a 32D is the equivalent cup volume on a tighter band.
Signs of a poor fit
- Band riding up at the back — band too large
- Shoulder straps carrying the weight — band too large; the band should do most of the support
- Spilling over the top or sides — cup too small
- Gaping or wrinkling fabric in the cup — cup too large
- Underwire sitting on breast tissue rather than against the ribcage — cup too small
Sizing varies between brands
There is no enforced international standard, and UK, US, EU and Australian systems all label differently — particularly above a D cup, where the letter sequences diverge. Treat a calculated size as a starting point for trying things on, not a fixed answer, and expect to vary by a size between brands and even between styles from the same brand.