You will get five picture mats cut for 13x19 pictures. They will fit into any 18x24 frames The opening is cut to 12.5 x 18.5 to overlap a 13x19 picture. The overlap also helps to mount pictures to the back These mats are acid free and cut from 4 ply mat board All of our matting is cut from high quality 4 ply acid free mat board. Each mat is precision cut with beveled edges that show off the beautiful white core of the mat board.