The dimensions of the window inserts vary depending on the panel type. The dimensions for standard short panel are 18 1/4" x 10 9/16", standard long panel are 39 1/16" x 10 9/16", architectural short panel are 17" x 13 9/16", architectural long panel are 39 7/16" x 13 5/8", architectural Arch 1 are 39 1/2" x 13 1/2", and architectural Arch 2 are 39 1/2" x 13 9/16".