Photo: Jim Harper / Wikimedia Commons (CC BY-SA 2.5)
A carat is the standard unit for measuring a diamond's weight — one carat equals 200 milligrams, roughly the weight of a paperclip's tip. Larger stones are described in carats and points, with 100 points making one carat, and most engagement-ring diamonds weigh between half a carat and two carats.
Carat weight is one of the "four Cs" jewelers use to value diamonds, alongside cut, color and clarity. The Fantasy Bra's center stone alone weighs 75.54 carats — heavier than almost any diamond ring ever made, and worth millions on its own.