Getting the rough opening right is one of the most important framing steps for doors and windows. Too tight and nothing fits; too loose and you'll struggle with shimming and insulation. This calculator gives you the correct rough opening for standard sizes.
Opening Type
Nominal Dimensions
in
in
Door
Scenario: You're framing for a 32 x 80 inch interior door.
Result: Rough opening: 34 inches wide (32 + 2) x 82.5 inches tall (80 + 2.5). Header length: 40 inches (34 + 6 for jack studs).
Window
Scenario: You're framing for a 36 x 48 inch replacement window.
Result: Rough opening: 36.5 inches wide (36 + 0.5) x 48.5 inches tall (48 + 0.5). Header length: 42.5 inches (36.5 + 6 for jack studs).
The rough opening is the framed hole in the wall where a door or window will be installed. It's slightly larger than the door/window unit to allow room for shimming, leveling, and insulation. For doors, add about 2 inches to width and 2-2.5 inches to height.
For interior doors: add 2 inches to the width and 2.5 inches to the height. For exterior doors: add 2-3 inches to width and 2.5-3 inches to height. These extra inches accommodate the door frame, shims, and insulation.
A 36-inch door needs a rough opening of 38 inches wide by 82.5 inches tall. This gives you 1 inch of clearance on each side for the door jamb and shims, and 2.5 inches above for the head jamb and gap.
For most windows, add 0.5 inches to both the width and height of the window unit. Some manufacturers specify exact rough openings -- always check the installation guide for your specific window before framing.
Want to learn more before you start your project?
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