Get exact rough opening dimensions, header sizes, and framing specs for any window or door.
Select whether you're framing a window, exterior door, or interior door using the tabs above. Enter the nominal unit size (the size printed on the product label or your plans — not the rough opening), choose your wall framing type (2×4 or 2×6), and select your load conditions. Hit Calculate to instantly get the exact rough opening width and height, recommended header lumber size, and a complete framing summary.
Getting rough opening sizes right is one of the most consequential things you'll do on a framing project. Too small, and you can't get the window or door unit into the wall — you'll need to tear out framing and redo it. Too large, and you'll have excessive shimming, potential structural problems, and a sloppy install that can void the manufacturer's warranty.
Consider a typical 36×80 exterior door: the correct rough opening is 38″ wide × 82½″ tall — but many first-time framers accidentally make it 36×80 (the door size) or use the wrong clearance. With a 2×6 load-bearing wall and a two-story house, that door also needs a doubled 2×10 header, not the undersized 2×6 a novice might grab. Mistakes like these cost hours of rework and hundreds of dollars in lumber.
Professionals use 1½″ of total width clearance and 1½″–2″ of height clearance for windows. Exterior doors get 2″ of width clearance and 2½″ of height. Interior doors are tighter — typically 2″ width and 2″ height. Header sizing depends on span and load, governed by the IRC span tables. This calculator bakes all of that in so you don't have to look it up every time.
For Windows:
For Exterior Doors:
For Interior Doors:
Header Sizing follows IRC Table R602.7. Span is the R.O. width. Load = 1 or 2+ stories of bearing load. A wider span and greater load requires a deeper header lumber (e.g., 2×10 or 2×12 doubled).
A rough opening (R.O.) is the framed opening in the wall — the space between the king studs and trimmer studs — into which a pre-hung window or door unit is installed. It is always larger than the finished unit to allow room for the frame, shimming, and adjustment.
For windows, the rough opening is typically 2″ wider and 2″ taller than the nominal unit size. Exterior doors get 2½″ of additional width and height. Interior doors are usually 2″ wider and 2″ taller. Always verify with the manufacturer's installation guide for exact clearances.
Header size depends on the span (rough opening width), the number of stories bearing on the wall, and local codes. Common guidelines: up to 3'6″ span use 2×6, 3'6″–5′ use 2×8, 5′–6'6″ use 2×10, and 6'6″–8′ use 2×12, all doubled with a ½″ spacer. This calculator recommends sizes based on IRC span table guidelines.
The rough opening width and height stay the same regardless of wall depth. The wall depth (2×4 vs 2×6) affects the extension jambs needed for the window/door trim, and the header construction (the OSB spacer thickness changes), but not the actual framed opening dimensions.