The print dimensions listed are for the size of paper it is printed on including the white border. All frames and mattes adds to the sizing.
Size example 1: On a 10x8", the printed area is 7x5" which leaves a 1.5" white border.
Size example 2: On a 10x8" print with a matte, the matte will have outside dimensions of 13x11".
Size example 3: On a 20x16" print with a matte and frame, the frame will have outside dimensions of 24x20".