Header Size Calculator
Header sizes for exterior bearing wall openings from IRC 2021 Table R602.7(1), and for open porch headers from Table R602.7(3), with the required jack studs returned beside every span. Two, three and four ply members from 2x4 to 2x12, indexed on ground snow load, building width and what the wall is carrying.
This is the lookup for a window, a door or a garage opening in a wall that carries load, where the snow-load column decides the answer and a habit from the last jurisdiction does not.
Same window, same lumber, three snow loads
- Double 2x10, exterior bearing wall, roof and ceiling only, 24 ft building width
- Ground snow 30 psf or less: 6 ft 10 in
- Ground snow 50 psf: 5 ft 11 in
- Ground snow 70 psf: 5 ft 3 in
Nineteen inches apart on the same header. A double 2x10 that cleared a 6 ft opening in one county will not clear it in another.
Four things that decide the header
Header size by snow load
Ground snow load is the column most people never look at, and it moves the answer more than anything except the floors above. IRC 2021 Table R602.7(1) tabulates 30 psf or less, 50 psf and 70 psf, and a double 2x10 over an exterior opening at a 24 ft building width reads 6 ft 10 in, 5 ft 11 in and 5 ft 3 in across those three. Carrying a remembered header size across a state line is how an opening fails plan review, and it is a cheap mistake to avoid.
What the wall carries above the opening
Roof and ceiling only is the easy case. Add one clear-span floor and that same double 2x10 at 24 ft and 30 psf falls from 6 ft 10 in to 5 ft 0 in. Make that floor centre-bearing instead and it recovers to 5 ft 8 in, because a centre-bearing floor delivers less load to the outside wall. Two clear-span floors take it down to 3 ft 10 in. The table has a separate column for each of those five cases, so match the one you actually have.
Depth, plies and the double 2x12 header max span
On an exterior wall carrying roof and ceiling at 24 ft and 30 psf, a double 2x6 reads 4 ft 7 in, a double 2x8 reads 5 ft 9 in, a double 2x10 reads 6 ft 10 in and the double 2x12 header max span is 8 ft 1 in. Adding plies helps, but the table caps at four, and a garage door header beam span of 16 ft is not in these tables at any ply count. That is an engineered member. All of this sits under IRC R602.7.
How many jack studs a header needs
The jack stud count is printed in the table beside the member, not calculated separately, and this tool returns it with every span. It is not constant: a double 2x8 at 24 ft and 30 psf takes one jack per end while a double 2x10 in the same wall takes two, and the same double 2x10 at a 12 ft building width drops back to one. King studs run full height beside the jacks either way, cripple studs above carry nothing, and the table keys on the stories supported.
Non bearing wall header, and when there is no header at all
IRC 2021 R602.7.4 permits a single flat 2x4 over openings up to 8 ft in nonbearing walls, provided the studs above are supported, so no structural header is required there at all. Confirm the wall is genuinely nonbearing first, because a wall running perpendicular to the joists near mid-span usually is not. Everything else on this page assumes a bearing wall. An insulated header does not change any of it either: capacity comes from the lumber plies and the foam filler carries nothing, so size from the table and then decide the cavity fill for your energy code.
Two IRC tables, and the jack studs printed beside them
Most header size calculators on the web will not tell you which code edition they run, which table the number came from, or whether the transcription was ever verified. Here is ours in full.
Exterior walls and porches
The dataset carries IRC 2021 Table R602.7(1) for exterior bearing walls across three ground snow loads and five support conditions, and Table R602.7(3) for open porch headers indexed on porch depth rather than building width.
Verified against the code text
Values were taken from the 2021 Seattle Residential Code Chapter 6 PDF, pages 6-15 to 6-17, which reproduces these IRC tables verbatim with no local amendments in them, and were checked against that printed text rather than retyped from a summary.
Grade, stated plainly
The IRC prints a single combined value for Douglas Fir-Larch, Hem-Fir, Southern Pine and SPF at No.2, so species does not move the answer here the way it does on a floor joist. No.2 is the only grade these tables carry.
4’-7″
One jack stud each end. Enough for a small window and very little else.
5’-9″
Still one jack per end, and the usual answer for a standard bedroom window.
6’-10″
Two jacks per end now. This is the header size for 6 foot window openings.
8’-1″
The deepest two-ply the table carries on this line. Beyond it, add plies.
All four are No.2 sawn lumber in an exterior bearing wall carrying roof and ceiling only, at a 24 ft building width and 30 psf ground snow. Narrow the building to 12 ft and that double 2x10 reaches 9 ft 0 in; widen it to 36 ft and it falls to 5 ft 9 in. Building width and snow load are the two columns people skip.
Code edition, and who actually decides
This tool runs the 2021 IRC tables. The edition your building department has adopted may be older, and states and municipalities amend the model text, so a locally amended table beats anything on this page. IRC R104 and R106 give the building official the authority, and the AHJ is the final word on your permit. A prescriptive header table is a worst-case lookup, not an engineering calculation, and nothing here is a stamped design. The table also stops applying the moment a point load from a post, a girder end or a ridge beam reaction lands over the opening, because these tables assume uniformly distributed load. That condition needs an engineered header and a verified load path through the jacks to the foundation.
Sources
- ICC Digital Codes — 2021 International Residential Code, Chapter 6, Wall Construction, for Tables R602.7(1) and R602.7(3), and sections R602.7 and R602.7.4.
- 2021 Seattle Residential Code, Chapter 6 (PDF), pages 6-15 to 6-17, which reproduces these IRC tables verbatim and was the text the dataset was verified against.
Data retrieved 4 September 2026. Deliberately absent: no garage door header size chart beyond what the IRC tabulates, because a typical 16 ft garage opening leaves these tables entirely; no LVL, LSL, PSL, glulam or steel headers, because the IRC does not tabulate engineered members; no interpolation between the 12, 24 and 36 ft building width columns, because the tool rounds up to the next tabulated bucket instead.
Header sizing FAQs
What size header do I need over a 6 ft window in a load-bearing exterior wall?
Read it off IRC 2021 Table R602.7(1) using building width, ground snow load and the number of floors supported. A double 2x10 covers 6 ft 10 in at a 24 ft building width carrying roof and ceiling at 30 psf, and the table returns the jack studs with it. Do not carry a double 2x10 habit across jurisdictions, because the snow-load column changes the answer.
Does Table R602.7(1) account for eave-side versus gable-side walls?
The table indexes on building width measured perpendicular to the roof ridge per its footnote, which is the eave-side condition. There is no separate gable-side table. Gable-end walls typically carry far less roof load, so using the table there is conservative but not wrong. Where the geometry is unusual, size it by calculation instead.
Do I need a header in a non bearing wall under the IRC?
No structural header is required. IRC 2021 R602.7.4 allows a single flat 2x4 for openings up to 8 ft in nonbearing walls, provided the studs above are supported. Confirm the wall is truly nonbearing first; a wall running perpendicular to the joists near mid-span often is not, and that mistake is expensive after drywall.
What is the double 2x12 header max span?
On an exterior bearing wall carrying roof and ceiling only, at a 24 ft building width and 30 psf ground snow, a double 2x12 reads 8 ft 1 in. Change any one of those three inputs and the number moves, so run your actual condition rather than treating 8 ft as a rule. Add plies or depth when the opening is wider.
Is there a garage door header size chart I can use?
Not a useful one, because a typical 16 ft garage opening is outside the IRC header tables at every tabulated ply count. Narrow single-car openings can sometimes be read from Table R602.7(1), but a double garage header is an engineered member, usually LVL, PSL or steel, sized by a manufacturer chart or an engineer with a matching load path below it.
Does an insulated header change the span?
No. Insulated headers are an energy-code and thermal-bridging question, not a structural one. Capacity comes from the lumber plies; the foam filler carries nothing. Size from the IRC table first, then decide the cavity fill for the energy code that applies to your job.
Sizing the header is free. Filling next month is not
Which is why it matters that the homeowners calling you about windows, doors and openings are the ones ready to buy the whole job. Filtering for that before the site visit is a marketing problem, not a framing one.
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