What determines the nipple size the patient ends up with?

Prior to surgery, your plastic surgeon should discuss your preference with you and then mark your breasts accordingly.  Once you have approved the size, then surgery can proceed.

We have nipple markers that we use in surgery to give us a perfectly round areola.  They typically are either 38mm, 40mm, or 42mm.  Therefore there is some small variation in the sizes we can choose.

The nipple areolar size can be varied somewhat based on preference.  Common diameters range from 38 to 42 mm (about 1.5 inches).  If you have a preference, you could certainly discuss it with your plastic surgeon.  It would be possible to say "I would like it a little larger (or smaller)" but there are limits.I hope that answers your question.  Look online at descriptions and drawings of the procedure.  That may help you understand how the nipple areolar size is an overall part of the breast reduction design.