Craft Mirrors with Flat Backs Mirrors come in bundles of different quantity depending on the size: 6" : 4 mirrors/unit 8": 4 mirrors /unit 10": 4mirrors/unit 12": 4 mirrors/unit 14":4 mirrors/unit Custom: 4 pieces of the sizes specified in the personalization text box. Each mirror is 2mm thick. For square size measures the length of each side, and for round mirrors, the size measures the diameter.