Door Rough Opening Calculator

A rough opening is the framed opening in a wall where a door (or window) will be installed. Getting the rough opening dimensions correct is essential — too small and the door will not fit, too large and you waste material on shimming and may compromise structural integrity.

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: Require double the door width plus additional framing

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, the header must be engineered based on the span and load — typically doubled 2×6, 2×8, 2×10, or 2×12 depending on the opening width and structural requirements.

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.