Header size comes from span and what sits above it
Two things set the size: how wide the opening is, and how much weight the wall carries. A quick field rule for load-bearing walls is that a header spans roughly its depth in inches, in feet — a 2x8 (about 8″ deep) covers about 8 feet before loads are added.
That is only a starting point. A load-bearing wall carrying floors above needs a taller header for the same span, and heavy snow country adds more still. The table below is the practical shortcut.
Common header sizes by span and load
| Opening span | Non-bearing | Bearing (roof + floor) | Bearing (2 floors + roof) |
|---|---|---|---|
| 3–4 ft | 2x4 | double 2x6 | double 2x8 |
| 5–6 ft | 2x4 | double 2x8 | double 2x10 |
| 7–8 ft | 2x4 | double 2x10 | double 2x12 |
| 9–10 ft | consult | double 2x12 | LVL / engineer |
| 11–12 ft | consult | LVL | engineer |
"Double" means two boards nailed together with a 1/2″ spacer so the header matches a 2x4 wall's thickness. Heavy snow load bumps these up about one size; verify against your local IRC span tables.
Details that keep the header sound
- Bearing at the ends. Each end needs at least 1.5″ of solid bearing on a jack (trimmer) stud — the IRC minimum.
- Non-bearing walls carry only the wall above, so the IRC allows a flat 2x4 up to 8 feet with no structural header.
- Snow load is real weight on the roof. Cold-climate openings can need a header 15 to 30 percent deeper.
- Undersizing shows up later as sagging, cracked drywall and doors that stick. Size for the actual load, not the door.
Common questions
What size header do I need for a 6 foot door opening?
On a load-bearing wall carrying a roof and one floor, a doubled 2x8 typically spans 6 feet. Carrying two floors and a roof it steps up to a doubled 2x10. On a non-load-bearing wall a 2x4 is enough up to 8 feet.
How do I know if the wall is load-bearing?
If joists, rafters or trusses land directly over the opening, the wall carries load. Exterior walls running perpendicular to the roof framing usually do too. When in doubt, ask an inspector or engineer before you cut.
When do I need an engineer instead of a span table?
Once a load-bearing opening passes about 8 feet, or when loads are unusual, get an engineer. Wide spans often move to an LVL or steel beam, which deflects far less than doubled dimensional lumber.
