A header's size depends on its span, what the wall above carries, the building width, and the ground snow load. For sawn lumber in a load bearing wall, 2021 IRC Table R602.7(1) (exterior walls) and Table R602.7(2) (interior walls) give the maximum span for each header size and the number of jack studs needed at each end.
Headers are the short beams over window, door, and garage openings. They collect the load that the studs would otherwise carry and deliver it to the sides of the opening. On a floor framing plan they show up wherever a bearing wall has an opening, so the size has to be settled before the plan is final. If you are still working out which walls carry load, start with load-bearing walls in a floor framing plan.
Header anatomy: king, jack, and cripple studs
A framed opening in a bearing wall has five parts:
- Header: the beam over the opening, usually two or more 2x members on edge with a spacer to match the wall thickness, or a single engineered member.
- Jack studs (also called trimmers): short studs under each end of the header that carry its load down to the bottom plate. The table tells you how many.
- King studs: the full-height studs beside the jack studs, nailed to the ends of the header. The code calls these full-height studs.
- Cripple studs: short studs above the header (up to the top plate) and below a window sill (down to the bottom plate), kept at the same spacing as the wall studs.
- Sill: the flat member at the bottom of a window rough opening.
For how openings fit into the rest of the wall, see wall framing basics and stud spacing.
How to read the IRC header span table
Table R602.7(1) is a large grid. Read it in this order:
- Supporting (the row group): what the header carries. The groups are roof and ceiling; roof, ceiling and one center-bearing floor; roof, ceiling and one clear-span floor; roof, ceiling and two center-bearing floors; and roof, ceiling and two clear-span floors.
- Ground snow load (the top column group): 30, 50, or 70 psf. Footnote e says to use the 30 psf columns where the ground snow load is less than 30 psf and the roof live load is 20 psf or less.
- Building width (sub-columns): 12, 24, or 36 feet, measured perpendicular to the ridge. Footnote c permits interpolation between widths.
- Size: written as number of plies and lumber size.
2-2 × 10means two 2x10s;1-2 × 8means a single 2x8. - Span and NJ: the maximum header span in feet and inches, and the number of jack studs at each end.
Footnote b states the spans are based on No. 2 grade Douglas fir-larch, hem-fir, Southern pine, and spruce-pine-fir. Footnote f matters for garage doors and tall walls: the spans assume the top of the header is laterally braced by perpendicular framing. Where it is not (for example, cripple studs bearing on the header), spans for 2x8, 2x10, and 2x12 headers must be multiplied by 0.70, or the header must be designed.
Header size chart: exterior bearing walls, roof and ceiling only
Slice of 2021 IRC Table R602.7(1). No. 2 grade DF-L, HF, SP, SPF. Exterior bearing wall supporting roof and ceiling only, 30 psf ground snow load. Spans in feet-inches; NJ = jack studs at each end. Footnote f reduction not applied.
| Size | 12 ft wide: span | NJ | 24 ft wide: span | NJ | 36 ft wide: span | NJ |
|---|---|---|---|---|---|---|
| 2-2x4 | 4'-0" | 1 | 3'-1" | 1 | 2'-7" | 1 |
| 2-2x6 | 6'-0" | 1 | 4'-7" | 1 | 3'-10" | 1 |
| 2-2x8 | 7'-7" | 1 | 5'-9" | 1 | 4'-10" | 2 |
| 2-2x10 | 9'-0" | 1 | 6'-10" | 2 | 5'-9" | 2 |
| 2-2x12 | 10'-7" | 2 | 8'-1" | 2 | 6'-10" | 2 |
| 3-2x8 | 9'-5" | 1 | 7'-3" | 1 | 6'-1" | 1 |
| 3-2x10 | 11'-3" | 1 | 8'-7" | 1 | 7'-3" | 2 |
| 3-2x12 | 13'-2" | 1 | 10'-1" | 2 | 8'-6" | 2 |
| 4-2x8 | 10'-11" | 1 | 8'-4" | 1 | 7'-0" | 1 |
| 4-2x10 | 12'-11" | 1 | 9'-11" | 1 | 8'-4" | 1 |
| 4-2x12 | 15'-3" | 1 | 11'-8" | 1 | 9'-10" | 2 |
Header size chart: roof, ceiling, and one center-bearing floor
Slice of 2021 IRC Table R602.7(1). No. 2 grade DF-L, HF, SP, SPF. Exterior bearing wall supporting roof, ceiling and one center-bearing floor, 30 psf ground snow load. Spans in feet-inches. Footnote f reduction not applied.
| Size | 12 ft wide: span | NJ | 24 ft wide: span | NJ | 36 ft wide: span | NJ |
|---|---|---|---|---|---|---|
| 2-2x4 | 3'-3" | 1 | 2'-6" | 1 | 2'-2" | 1 |
| 2-2x6 | 4'-10" | 1 | 3'-9" | 1 | 3'-3" | 2 |
| 2-2x8 | 6'-1" | 1 | 4'-10" | 2 | 4'-1" | 2 |
| 2-2x10 | 7'-3" | 2 | 5'-8" | 2 | 4'-10" | 2 |
| 2-2x12 | 8'-6" | 2 | 6'-8" | 2 | 5'-8" | 2 |
| 3-2x8 | 7'-8" | 1 | 6'-0" | 1 | 5'-1" | 2 |
| 3-2x10 | 9'-1" | 1 | 7'-2" | 2 | 6'-1" | 2 |
| 3-2x12 | 10'-8" | 2 | 8'-5" | 2 | 7'-2" | 2 |
| 4-2x8 | 8'-10" | 1 | 6'-11" | 1 | 5'-11" | 1 |
| 4-2x10 | 10'-6" | 1 | 8'-3" | 2 | 7'-0" | 2 |
| 4-2x12 | 12'-4" | 1 | 9'-8" | 2 | 8'-3" | 2 |
The same table continues with 50 and 70 psf columns, single-ply headers, clear-span floors, and two floors. Spans drop as snow load, building width, and supported floors increase, so do not reuse these values outside the stated row and column.
Interior bearing wall headers
Interior bearing walls use Table R602.7(2), which has no snow load columns because the header carries floor load only.
Slice of 2021 IRC Table R602.7(2). No. 2 grade DF-L, HF, SP, SPF. Interior bearing wall supporting one floor only. Spans in feet-inches.
| Size | 12 ft wide: span | NJ | 24 ft wide: span | NJ | 36 ft wide: span | NJ |
|---|---|---|---|---|---|---|
| 2-2x6 | 6'-1" | 1 | 4'-4" | 1 | 3'-6" | 1 |
| 2-2x8 | 7'-9" | 1 | 5'-5" | 1 | 4'-5" | 2 |
| 2-2x10 | 9'-2" | 1 | 6'-6" | 2 | 5'-3" | 2 |
| 2-2x12 | 10'-9" | 1 | 7'-7" | 2 | 6'-3" | 2 |
| 3-2x10 | 11'-5" | 1 | 8'-1" | 1 | 6'-7" | 2 |
| 3-2x12 | 13'-6" | 1 | 9'-6" | 2 | 7'-9" | 2 |
Window header size: a worked lookup
Take a window in the exterior wall of a 36-foot-wide two-story house. The first floor wall carries the roof, the ceiling, and a second floor that has a center bearing wall. Ground snow load is under 30 psf and roof live load is 20 psf, so the 30 psf columns apply. Reading the 36-foot column of the second table: two 2x10s are good for 4'-10" with two jack studs each end; two 2x12s reach 5'-8", also with two jack studs. If the window sits lower with cripples between the header and the top plate, check footnote f before relying on either number.
Door header size chart and garage door headers
Doors use exactly the same tables as windows; the opening type does not change the lookup. What changes is the width.
Garage doors are where sawn lumber runs out. The longest span anywhere in Table R602.7(1) is 15'-3" (four 2x12s, roof and ceiling only, 12-foot building width, 30 psf). A typical 16-foot two-car door is wider than every entry, so it needs an engineered header such as LVL, PSL, or glulam, or a design by an engineer. Single garage doors can sometimes be met from the table, but garage walls are often tall with cripples above the header, which triggers the 0.70 factor in footnote f.
King studs at each end
Section R602.7.5 requires headers to be supported on each end by jack studs or approved framing anchors per the NJ column, and Table R602.7.5 sets the minimum number of full-height (king) studs at each end in exterior walls.
2021 IRC Table R602.7.5, minimum full-height studs at each end of headers in exterior walls.
| Maximum header span | < 140 mph Exp. B or < 130 mph Exp. C | ≤ 115 mph Exp. B |
|---|---|---|
| 4 ft | 1 | 1 |
| 6 ft | 2 | 1 |
| 8 ft | 2 | 1 |
| 10 ft | 3 | 2 |
| 12 ft | 3 | 2 |
| 14 ft | 3 | 2 |
| 16 ft | 4 | 2 |
| 18 ft | 4 | 2 |
For spans between those listed, footnote a says to use the count for the larger span.
Headers in nonbearing walls
Section R602.7.4 says load-bearing headers are not required in interior or exterior nonbearing walls. A single flat 2x4 may be used as the header for openings up to 8 feet wide if the vertical distance to the parallel nailing surface above is not more than 24 inches, and no cripples or blocking are required above it. The hard part is confirming the wall really is nonbearing; walls under a ridge beam post, a girder truss, or floor joists that land on them are not.
Other header types in the code
- Single member headers (R602.7.1): a single header framed with a flat 2-inch nominal member or wall plate on the top and bottom, face nailed with 10d box nails at 12 inches on center.
- Rim board headers (R602.7.2): sized from Table R602.7(1), supported at each end by full-height studs.
- Wood structural panel box headers (R602.7.3 and Table R602.7.3): plywood or OSB faces nailed over a framed box. Spans are tabulated by header depth and house depth.
- Open porches: Table R602.7(3) gives girder and header spans for porch beams.
LVL headers use manufacturer tables
Every IRC header table assumes No. 2 sawn lumber. LVL, PSL, LSL, and glulam headers are sized from the manufacturer's span tables or software for the exact product, depth, and load case, and those documents also set bearing length and jack stud count. Do not read an LVL size off the IRC chart.
Use the table for the conditions it states
These are prescriptive limits for the stated species, grade, loads, and building width only. The adopted code edition and local amendments govern, so check with your building department. The full tables are in Chapter 6 of the 2021 IRC, and the American Wood Council span table resources cover other species and load cases. Point loads, girder trusses, and openings under beams need design.
Headers belong on the framing plan as a callout at each opening. Framing Plan lets you draw walls, openings, beams, and joist layouts and export them to PNG, PDF, or DXF as a preliminary drawing. The app does not size headers or check code spans; its bundled sample profile uses demo figures in metric, so take sizes from the table or the manufacturer and label them on the drawing yourself.