Framing a garage door opening is one of the most structurally demanding tasks in residential construction. Garage doors are wide, heavy, and require a beam strong enough to span the entire opening while supporting the roof load above. This guide covers garage door rough opening sizes, IRC header requirements, and the post sizing you need to do the job safely.
The rough opening for a garage door is typically 3 inches wider and 1½ inches taller than the door unit itself to allow for the door track hardware and leveling. Common standard sizes are:
Always verify the manufacturer's specified rough opening before framing—dimensions can vary by brand and model.
Because garage door openings span 9 to 18 feet, they require engineered lumber (LVL beams) in most cases. A standard double 2×12 is the minimum for a 9-foot opening in a non-load-bearing garage wall, but most building departments require a structural engineer's specification for anything over 10 feet wide. Common garage door header specs:
Support posts on each side of the garage door must be sized to carry the beam load. A minimum of two 2×6 king studs (or a 4×6 post) is typical for single-car openings; double-car openings often require a 4×6 or 6×6 post. Enter your garage door dimensions into the framing calculator and select "Garage Door" to get an automated materials estimate including posts, header, and cripple studs. Cross-reference the result with the header size reference table for a sanity check.