White Picture Mats 18×24″ Picture Mats with core bevel cut for 16×20″ Pictures. Cream white picture frame mats size 18×24 inch with opening size 15.5×19.6 inches for 16×20 inches Pictures. The photo mats are beveled cut with white core and 4-ply thick (about 1.4 mm or 1/16 inch). Perfect for framing 16×20 photo in an 18×24 picture frame. Great decoration for your frames and photos. Package included: 12pcs white 18×24 picture mats.