When you cut studs out of a load-bearing wall to make a door or window, the load those studs carried — roof, ceiling, the floor above, snow on the roof — has to go somewhere. The header (also called a lintel) picks up that load and carries it sideways to the jack studs at each end of the opening, which carry it down to the bottom plate and the floor or foundation. That chain is called the load path. Every piece has to be there and in contact: a gap between the header and a jack stud is a gap in the load path.
How headers are built
Most site-built headers are made of two or three pieces of 2× lumber on edge, nailed together. The thickness of the assembly matches the wall:
- 2×4 wall (3 1/2″ thick): two plies of 2× (3″) plus a 1/2″ plywood or OSB spacer between them. Without the spacer the header is 1/2″ shy of the face of the wall and drywall or sheathing won't land flat.
- 2×6 wall (5 1/2″ thick): three plies (4 1/2″) plus spacers, or two plies with rigid insulation between them to reduce the thermal bridge.
The calculator uses two plies for 2×4 walls and three for 2×6 walls when it counts lumber. A header is cut to the rough opening width plus one jack stud thickness on each side (1 1/2″ each), because it sits on top of the jacks.
Other options include solid sawn 4× or 6× timbers, engineered lumber (LVL, PSL, LSL) for longer or heavier spans, and insulated box headers built from plywood webs. Engineered lumber comes with the manufacturer's own span tables.
Depth, span and jack studs
A deeper header is much stiffer and stronger: bending strength grows with the square of the depth and stiffness with its cube. That is why a 2×12 header can span far more than a 2×6 of the same species. The required depth depends on:
- the opening width (span);
- what the wall supports — roof and ceiling only, one floor, two floors — and the building width, which sets how much roof or floor is resting on the wall;
- the ground snow load where you live;
- the species and grade of the lumber.
The IRC handles this with header span tables (Table R602.7(1) for exterior bearing walls and R602.7(2) for interior bearing walls). For each combination they list the maximum span of each header size and how many jack studs it needs at each end. Wider and more heavily loaded headers need two jacks per side because a single 1 1/2″ jack doesn't give the header enough bearing area — the wood fibres would crush.
This site deliberately does not pick a header size for you. Getting it right needs the loads above, and a wrong guess is a structural problem, not a waste problem. Choose the size from your plans, the code table that applies in your area or your engineer, and the calculator will count the plies and stock lengths. It defaults to one jack per side and two for openings over 6 feet — a common pattern, but your table governs.
Filling the space above the header
In an 8 ft wall with 82 1/2″ door openings, the gap between the top of a header and the top plates is about 11 5/8″. You can fill it with cripples on layout (short studs), or make the header deep enough to fill it: two 2×12s (11 1/4″) nearly close the gap and save cutting a lot of short cripples. Many framers build every exterior header from 2×12 for exactly that reason, even if a smaller size would carry the load. The downside is a larger thermal bridge in insulated walls, which is why energy-focused builders use the smallest header the table allows plus cripples or insulated box headers.
Non-bearing walls
Interior partitions that don't carry joists, rafters or a floor above don't need structural headers. The IRC allows a single flat 2× (laid with the wide face down) over openings in non-bearing walls within limits — see section R602.7.3. It still gives you a nailing surface for drywall and door trim. Choose "Flat 2×" in the calculator for those openings.
If you are removing or widening an opening in an existing load-bearing wall, a header is only part of the job: the load has to be supported temporarily while you work, and the jacks must bear on something solid all the way down to the foundation. That is a job to plan with a professional.
Header checklist
- Size from the plans, the applicable code table or an engineer — not from a rule of thumb.
- Plies and spacer make the header flush with both faces of the wall.
- Header length = rough opening + 2 × jack thickness (+ 3″ for one jack each side).
- Jacks tight under both ends; number of jacks per the table.
- Kings nailed to the header ends and both plates.
- Crown (the slight bow) of each ply facing up.
Add your openings and header sizes in the wall framing calculator, or read how to frame a rough opening for the cut lengths.
Planning information only — framing and deck requirements vary by jurisdiction. Verify with your local building code or a licensed professional.