Door & Window Rough Opening Calculator
Pick a door or window and see the rough opening, the header from a simplified IRC span table, the king, jack and cripple studs, and a cut list, drawn as a framed wall you can turn around.
- Rough opening—
- Header—
- King / jack studs—
- Cripples—
Drag to turn · scroll or pinch to zoom · the orange block is the rough opening · turn on sheathing or drywall to see the wall skins
How this rough opening calculator works
Doors: a prehung door arrives in its own frame. The rough opening is the door size plus 2 in in width and 2-1/2 in in height, which leaves room for the jambs, shims and (on an exterior door) the threshold. Sliding patio doors and bifold doors are about +2 in each way. A pocket door needs twice the door width plus 1 in, and 4-1/2 in extra height for the track.
Windows: the common starting point is the frame size plus 1/2 in each way. Window makers publish their own rough opening, and it can be different, so the maker's number always wins.
Header: the span table is IRC Table R602.7(1) for exterior bearing walls, for Douglas fir-larch, hem-fir and SPF No. 2 lumber, 30 psf ground snow load, with the top of the header braced by framing above. Building widths of 28 and 36 ft share the same values. The tool picks the smallest two-ply header whose span reaches your opening. For a nonbearing wall the IRC lets you use a single flat 2×4 as the header for openings up to 8 ft wide (R602.7.4).
Studs: kings run full height and jacks carry the header. This tool uses one jack per side for short openings and two for longer ones; the table's own jack-stud column controls, so read it for your case. Cripples keep the stud layout going above the header and below a window sill.
Limits to know
- This is a simplified lookup, not a structural design. Southern pine, other grades, floors above two stories, heavy snow, wind or seismic loads and point loads from beams or girders all change the answer. Your building department or a structural engineer has the final say.
- Houston's design snow load is far below the 30 psf column used here, so the table is on the safe side there. Ask your building department which code year and local amendments apply.
- For openings wider than the table's largest header, use an engineered header (LVL or steel) from the maker's span tables.
- A window or door in an exterior wall also needs flashing, a sill pan and the maker's install steps. Those are not covered here.
This tool is a planning aid, not a design. Check the unit maker's install sheet and your local building rules before you cut lumber.
Sources
- 2021 International Residential Code, R602.7 Headers (ICC)
- 2021 IRC Chapter 6 with Table R602.7(1) header spans (UpCodes viewer)
- Fine Homebuilding, The Right Header for Every Wall (nonbearing flat 2×4 rule)
- DoItYourself, prehung door rough opening: +2 in width, +2-1/2 in height
- Doors for Pros, how to measure a rough opening
- Teza Doors, bifold door rough opening sizes
- Gladiator Windows and Doors, bifold rough opening guide
- Softly Outdoor, standard patio door sizes and rough openings
Estimates only — not engineering, legal or code advice. Check requirements with your local building department and a licensed professional before you build.
Common questions
What is the rough opening for a 3068 (36 × 80 in) exterior prehung door?
Add 2 in to the width and 2-1/2 in to the height of the door size. A 3068 door is 36 × 80 in, so the rough opening is 38 × 82-1/2 in. The extra height leaves room for the threshold and shims. Check the door maker's install sheet, because its printed rough opening wins.
What is the rough opening for a 2868 interior prehung door?
A 2868 door is 32 × 80 in, so with the usual +2 in width and +2-1/2 in height the rough opening is 34 × 82-1/2 in. In a nonbearing wall a single flat 2×4 can serve as the header for openings up to 8 ft wide (IRC R602.7.4).
How big should a window rough opening be?
A common starting point is the window frame size plus 1/2 in in each direction. A 36 × 48 in window gets a 36-1/2 × 48-1/2 in opening. Window makers publish their own rough opening, and it can differ, so use theirs. The tool lets you type the maker's numbers in.
What header does a 38 in door opening need in a 2×6 exterior wall?
For an exterior wall that carries only the roof, in a building up to 28 ft wide, IRC Table R602.7(1) lets a built-up (2) 2×6 header span 3 ft 10 in (46 in). A 38 in opening fits that, so the tool shows a (2) 2×6 header with a jack stud at each end. The table uses 30 psf ground snow load, which is on the safe side for Houston.
What is the rough opening for a pocket door?
A pocket door needs room for the door to slide into the wall. The usual rule is twice the door width plus 1 in wide and the door height plus 4-1/2 in tall. A 2868 (32 in) pocket door gives a 65 × 84-1/2 in opening. Pocket door kits come with their own rough opening size, so follow the kit.
What are king studs, jack studs and cripples?
King studs run the full height of the wall on each side of the opening. Jack (trimmer) studs sit beside the kings and carry the header. Cripples are short studs above the header, or above and below a window, that keep the 16 in layout going. A window also has a flat rough sill under its opening.