HEADER SIZE
Header size chart — IRC Table R602.7(1)
Maximum header span in an exterior bearing wall carrying roof and ceiling only, at 30 psf ground snow. Jack studs required per side are in parentheses. Building width is the whole building measured perpendicular to the ridge — it moves the answer more than the opening width does, which is why a quick-pick chart with a single column per member is guessing at it.
| Header | 12 ft building | 24 ft building | 36 ft building |
|---|---|---|---|
| (1) 2×6 | 4'-0" (1) | 3'-1" (2) | 2'-7" (2) |
| (1) 2×8 | 5'-1" (2) | 3'-11" (2) | 3'-3" (2) |
| (1) 2×10 | 6'-0" (2) | 4'-8" (2) | 3'-11" (2) |
| (1) 2×12 | 7'-1" (2) | 5'-5" (2) | 4'-7" (3) |
| (2) 2×4 | 4'-0" (1) | 3'-1" (1) | 2'-7" (1) |
| (2) 2×6 | 6'-0" (1) | 4'-7" (1) | 3'-10" (1) |
| (2) 2×8 | 7'-7" (1) | 5'-9" (1) | 4'-10" (2) |
| (2) 2×10 | 9'-0" (1) | 6'-10" (2) | 5'-9" (2) |
| (2) 2×12 | 10'-7" (2) | 8'-1" (2) | 6'-10" (2) |
| (3) 2×8 | 9'-5" (1) | 7'-3" (1) | 6'-1" (1) |
| (3) 2×10 | 11'-3" (1) | 8'-7" (1) | 7'-3" (2) |
| (3) 2×12 | 13'-2" (1) | 10'-1" (2) | 8'-6" (2) |
| (4) 2×8 | 10'-11" (1) | 8'-4" (1) | 7'-0" (1) |
| (4) 2×10 | 12'-11" (1) | 9'-11" (1) | 8'-4" (1) |
| (4) 2×12 | 15'-3" (1) | 11'-8" (1) | 9'-10" (2) |
IRC 2021 Table R602.7(1), No. 2 grade, roof and ceiling only, 30 psf ground snow. Identical in the 2024 edition.
Adding a floor to the load path, or 50/70 psf ground snow, changes the member — often by a whole ply. Run your load case above.
About this calculator
This header size calculator reads IRC Table R602.7(1) for exterior bearing walls and Table R602.7(2) for interior bearing walls, and returns the smallest tabulated member that spans your opening along with the jack studs the code requires with it. Both tables are identical in the 2021 and 2024 editions. The two inputs most quick-pick charts leave out are the ones that move the answer most: building width and ground snow load. A 7-foot opening under a roof, ceiling and one center-bearing floor at 30 psf takes a double 2×10 on a 12-foot-wide building, a triple 2×10 at 24 feet, and a quadruple 2×10 at 36 feet — same opening, three different headers. Spans assume No. 2 grade Doug fir-larch, hem-fir, Southern pine or spruce-pine-fir. ESTIMATE ONLY — verify with an engineer or your local building official before framing.
How to use this calculator
Enter the rough opening width — the framed hole, not the door or window unit (a 36-inch door needs roughly a 38-inch rough opening).
Pick what the header actually carries. Roof and ceiling only is the lightest case. A clear-span floor loads the header harder than a center-bearing floor, because there is no interior wall picking up half the joist load. Interior bearing walls use a separate code table with no snow term.
Set the building width — the width of the whole building, perpendicular to the ridge, not the opening. This is the largest single driver of header size.
Set the ground snow load from your local building department.
The result gives the member, its published maximum span, and the jack studs required per side straight from the table cell. If the opening exceeds every tabulated member, the calculator says so rather than guessing — that opening needs an engineered LVL, PSL or steel beam.
Worked example
A 7-ft opening carrying a roof, ceiling and one center-bearing floor, 30 psf ground snow. Watch what building width alone does:
12-ft-wide building: (2) 2×10, max span 7.25 ft, 2 jack studs per side.
24-ft-wide building: (3) 2×10, max span 7.17 ft, 2 jack studs.
36-ft-wide building: (4) 2×10, max span 7.00 ft, 2 jack studs.
Same opening, same load path, same snow — three different headers, because a wider building puts more tributary roof and floor area on that header. Any chart that answers this with one number is guessing at your building width.
A 6-ft opening on that same 24-ft building: (3) 2×8, max span 6.00 ft, 1 jack stud.
A 12-ft opening on the 24-ft building: no sawn-lumber member in Table R602.7(1) reaches it — that is an engineered beam, and the calculator says so instead of returning a fourth ply and hoping.
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
Building width drives header size more than opening width does. Going from a 12-ft to a 36-ft building can cost you two extra plies on the same opening.
Read jack studs from the table cell, not from a width rule. The code varies the count by load case and building width — it is not simply 1 under 4 ft and 2 above.
A clear-span floor is a heavier case than a center-bearing floor, because no interior wall takes half the joist load.
Built-up header construction: plies of dimensional lumber with a ½-inch plywood spacer between, 16d nails in two rows at 16 in o.c.
Single-ply members appear in the code table and are legitimate, but they need packing out to match wall thickness.
When the table runs out, it runs out. Stacking a fifth ply is not a code-compliant substitute for an engineered LVL, PSL or steel beam.
Cripple studs above the header follow the wall stud spacing.
Common questions
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