Free Window & Door Calculator – Rough Opening & Trim
Calculate rough opening area and casing linear feet for windows and doors. Estimate trim board quantities for any room.
Window & Door Calculator Guide
The Window & Door Calculator estimates rough opening area and trim board quantities for window and door installations. Enter the dimensions and count for your windows and doors to calculate total opening area and casing linear feet.
Standard rough openings are 1/2 inch larger than the window unit on each side, and 2 inches wider and 2.5 inches taller than door slabs. Casing (trim) is installed around openings on one or both sides of the wall.
Trim boards come in standard lengths (8, 10, 12, and 16 feet). The calculator includes a 10% waste factor for miter cuts at corners. Always add 15% extra when budgeting for miter cuts and fitting adjustments.