Door Rough Opening Calculator

A rough opening is the framed opening in a wall where a door (or window) will be installed.
Too small and the door will not fit. Too large and you are packing the gap with shims, which is slow and never as solid.

Standard rough opening formula: The rough opening is always slightly larger than the actual door size to allow room for the door frame (jamb) and shimming space for plumb and level adjustment.

Rough Opening Width = Door Width + 2 inches (1 inch per side for jamb and shimming) Rough Opening Height = Door Height + 2.5 inches (for head jamb, shimming, and threshold)

For pre-hung doors (most common today), the manufacturer specifies the exact rough opening needed. These standard additions account for the jamb material (typically 3/4 inch per side) plus shimming clearance.

Standard door sizes (width × height):

• Interior doors: 24", 28", 30", 32", or 36" wide × 80" tall
• Exterior doors: 32" or 36" wide × 80" tall (or 96" for 8-foot doors)
• Double doors: Multiply the single door rough opening width by 2, minus 2 inches
• Pocket doors: Double the door width plus 1 inch across, and the door height plus 4-1/2 inches tall, because the header track and the frame kit live in that extra height

Common rough openings by door size:

• 24" door: 26" × 82.5" rough opening
• 28" door: 30" × 82.5" rough opening
• 30" door: 32" × 82.5" rough opening
• 32" door: 34" × 82.5" rough opening
• 36" door: 38" × 82.5" rough opening

Framing components around a door: The rough opening consists of king studs (full height from plate to plate), jack studs (trimmer studs that support the header), a header beam across the top, and a sole plate at the bottom (which is cut out for the doorway after framing).

Header sizing: The header above the door carries the load from above. For non-load-bearing interior walls, a single 2×4 laid flat is often sufficient.
For load-bearing walls it has to be sized against the actual span and load, which lands somewhere between a doubled 2×6 and a doubled 2×12.

The ladder this page uses is deliberately the conservative one, and it does not ask what is above the wall, so it assumes roof plus a floor. If you know what the header is carrying, the window header size calculator takes that as an input and will often name a shallower board for the same opening. Where the two disagree, build the deeper of the two headers and let your inspector talk you down.

Important installation notes: Always check that the rough opening is plumb (vertical sides are perfectly vertical) and level (the top is perfectly horizontal) before installing the door. Use a level on both sides and across the top. Shims are used to make fine adjustments during installation.