The diameter for these Christmas Ornament cutouts is 3-3/8 inches (85mm).  It produces an ornament that is roughly 3" in diameter after firing.  For instructions on how create ornaments, please see my video entitled: How to Make Porcelain Christmas Ornaments - Step by Step Workshop
 
You can shop for stamps that fit this 85mm cutout here.  No stamps are included with the cutout bundles.