23x31 Matting for Picture Frame Black with Cream Core and 19x27 Opening Size (B221MAT) MAT SIZE: This matting fits a 23x31 frame. (frame not included) OPENING SIZE: This mat fits a 19x27 photo / print. (Actual opening size is 18.5x26.5) Matting Material is Crescent Mat Board. Black Finish / Cream Core with White Backing (PH Neutral). This listing includes (1) Custom Cut Mat. (The size selected represents the OUTSIDE dimensions of the matting.)