How bra size is calculated
A bra size has two parts: the band and the cup. The band comes from your underbust measurement, rounded to the nearest even inch (or nearest 5 cm in EU sizing). The cup comes from the difference between your bust and band, each inch of difference is one cup letter, so a 3-inch difference is roughly a C cup.
How to measure
- Band: wrap the tape snugly around your ribcage, directly under the bust, level all the way round.
- Bust: measure around the fullest part, keeping the tape parallel to the floor and not too tight.
- Measure braless or in a thin, non-padded bra, standing relaxed.
Sister sizes and why they help
If the band digs in or rides up but the cups fit, try a sister size, the same cup volume on a different band (for example, 34C and 32D hold a similar cup). It's the quickest fix when a bra is almost right.
Why fit still beats the formula
Methods and brand cuts vary, so treat this as a starting point, not the final word. A good bra sits level, the band does the supporting, and the cups contain you without gaps or spillage. When in doubt, try a size up and down in the cup and band.