12mm round. These are premium Japanese cotton pearls made by Miyuki. Though named "Rich Grey", these pearls have a beautiful violet and light green hue in certain light. These pretties are actually made of compressed cotton and then coated with a reflective, shimmery pearl finish. This process produces a very solid and rock hard pearl bead that is light as a feather. These faux cotton pearls are very sturdy under normal wear. Did I mention that these are shimmery? Absolutely stunning.