Rough opening
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Door and window layout
Rough Opening Calculator
Size a door or window rough opening from the unit dimensions, clearance, and header bearing. Get the framing counts you need before cutting studs.
Units
Header cut length
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King studs
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Jack studs
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Rough opening is a layout check
Manufacturer rough-opening specs, local code, load path, hardware, flashing, fire rating, and header sizing override these defaults.
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Rough opening formula
Rough width = unit width + side clearance total
Rough height = unit height + top/bottom clearance total
Header length = rough width + 2 × bearing
King studs = 2 × quantity. Jack studs = 2 × jacks per side × quantity.
Example
A 36 in by 80 in prehung door with 2 in side clearance and 2.5 in height clearance needs a 38 in by 82.5 in rough opening. With 3 in bearing per side, header cut length is 44 in.
Rough opening FAQ
How much bigger should a rough opening be than a door?+
A common prehung interior door default is door slab width plus 2 inches and slab height plus 2.5 inches. Some exterior doors, pocket doors, fire doors, and manufacturer frames need different clearances, so check the product sheet before framing.
How much bigger should a rough opening be than a window?+
Many window makers call for about 0.5 inch clearance on each side and at the top and bottom, which means unit width plus 1 inch and unit height plus 1 inch. Manufacturer specs override any generic calculator default.
How do I calculate header length for a rough opening?+
Header length is rough opening width plus bearing at both ends. With 3 inches of bearing each side, a 38 inch rough opening uses a 44 inch header blank before job-specific trim or connection details.
Does this size the structural header?+
No. This lays out the opening width, height, studs, sill pieces, and header cut length. Header depth, load path, species, grade, fastening, wind, seismic, and local code still need product tables or engineering.