Plastic surgeons gauge droop based on the position of the nipple compared to the breast crease, also called the inframammary crease. The ideal position for the nipple is above the inframammary crease, but with time, age and gravity, the breast descends.
Mild droop is also called grade I ptosis or grade I breast droop.
Moderate droop is also called grade II ptosis or grade II breast droop.
Advanced droop is also called grade III ptosis or grade III breast droop, or severe droop.