Sister sizes are bra sizes that have the same cup volume but a different band size. If your usual size isn’t available, or you want to adjust the fit of the band, a sister size can be a great alternative.

Go down a band size and up a cup size for a firmer fit, or go up a band size and down a cup size for a looser fit.

For example, the sister sizes of a 34C are 32D and 36B.