HEADER SIZE
About this calculator
This header size calculator gives a quick IRC-style recommendation for the built-up header that spans a door or window opening in a wood-framed wall. Choose the wall location (non-bearing, exterior bearing, or interior bearing), the number of floors stacking on top of the wall, and the opening width — the calculator returns a built-up header size (e.g., "two 2x10s" or "three 2x12s") consistent with the simplified tables in IRC R602.7. Non-bearing partition walls take a minimum 2-2x4 header up to 8 ft. Bearing walls add depth as opening width and load increase: roof-only walls go up to 2-2x12 at 10 ft, while two-story bearing walls jump faster. ESTIMATE ONLY — IRC tables are based on specific assumptions (snow load, building width, lumber grade); your inspector or engineer is the final word.
How to use this calculator
Enter the rough opening width — the framed hole for the door or window unit, NOT the door size itself (a 36" door needs a ~38" rough opening). Pick the wall location: non-bearing partition walls only support themselves; exterior bearing walls support roof, ceiling, and any floors above; interior bearing walls run perpendicular to and support the floor joists above.
The calculator returns a built-up header recommendation (e.g., "two 2x10s") plus the number of jack studs needed on each side and the king stud count. For openings beyond standard ranges, the result will indicate "Engineered LVL/PSL required" — those need an engineer-stamped beam, not built-up dimensional lumber.
Worked example
A 6-ft sliding glass door in an exterior wall with one floor above:
Header: two 2x10s with ½-inch plywood spacer between. Jack studs: 2 per side. King studs: 1 per side. Total framing for this opening: 2 jacks + 1 king + header on each side, with cripples above the header up to the top plate.
The same 6-ft opening in a non-bearing partition: just two 2x6s. The opening doesn't carry roof or floor loads, so the header is much lighter.
A 10-ft garage door opening in an exterior wall with one floor above: three 2x12s, with engineer verification recommended at this width.
A 16-ft garage door opening: requires an engineered LVL or PSL beam — built-up dimensional lumber is impractical at this scale (would need 4+ plies of 2x12).
Common mistakes & waste factors
Confusing rough opening with door/window unit width. Always add jamb thickness, casing, and slip-fit allowance when sizing the rough opening. Standard add: door units +2 inches, window units +0.5 inch.
Forgetting jack studs. Jack studs support the header — single jack per side for openings under 4 ft, double jack per side for 4–8 ft, triple jack per side for over 8 ft. Skipping the doubled jacks on a 6-ft opening is a code violation.
Mixing up bearing wall types. Exterior walls supporting roof OR roof+1 floor OR roof+2 floors all use different headers — check what's actually above before choosing.
Using the IRC quick-pick on a snow-load region. IRC R602.7 simplified tables assume specific snow load, building width, and lumber grade. In high-snow regions or wide buildings, an engineer should size the header.
Rules of thumb
Jack studs per side: 1 for ≤4 ft, 2 for 4–8 ft, 3 for >8 ft.
Header depth scales with width: at 6 ft opening, 2x8 minimum; at 8 ft, 2x10; at 10 ft, 2x12; over 10 ft, switch to engineered LVL.
Built-up header construction: 2 or 3 plies of dimensional lumber + ½-inch plywood spacer between plies + 16d nails in 2 rows at 16" o.c.
Above 10 ft openings or 2 floors above: engineered LVL or PSL beam, not built-up dimensional lumber.
Cripple studs (the short studs above the header up to the top plate) follow the same on-center spacing as the wall studs.
Common questions
Tool and material links below are affiliate links — we may earn a small commission if you buy, at no extra cost to you.