Header Size Calculator
This free header size calculator sizes a door or window header the way a plans examiner checks it — from the IRC prescriptive span table, not a rule of thumb. Tell it the rough-opening width, the building width (measured perpendicular to the ridge), and what the header carries, and it returns the smallest built-up header from 2-ply 2×4 up to 4-ply 2×12 that spans the opening, using IRC Table R602.7(1) for a combined No. 2 species (Douglas fir-larch, hem-fir, Southern pine, spruce-pine-fir). Because the table uses one governing species column, there is no species to guess at.
It also gives you the two things people forget: the jack (trimmer) studs that carry the header ends — a value read straight from the table — and the king (full-height) studs from Table R602.7.5, which scale with the span and your wind exposure. It handles the IRC footnote (f) lateral-bracing rule too: if cripple studs bear directly on the header, the span of a 2×8, 2×10, or 2×12 is cut by 30 percent. When an opening is wider than the largest tabulated header, it says so and points you to an engineered beam instead of guessing.
It covers both IRC header tables — R602.7(1) for exterior bearing walls (ground snow 30, 50, and 70 psf, every supported condition from a roof-and-ceiling opening up to two floors) and R602.7(2) for interior bearing walls (one or two floors) — at building widths of 12, 24, and 36 feet, sizes from a single 2×6 to a 4-ply 2×12. Everything is transcribed verbatim from the official IRC tables. Sizing only — no pricing, no signup.
Header Size Calculator
Size a door or window header in a bearing wall — header size and ply, plus the jack (trimmer) and king (full-height) studs each end, straight from IRC Table R602.7(1) and R602.7.5. Free, no signup.
What are you solving for?
Find the smallest header for your opening, or the widest opening a header size can carry.
The wall & the load
Exterior bearing walls (Table R602.7(1), any snow load) and interior bearing walls (Table R602.7(2)) — pick the wall type, then what the header carries.
Values use the combined No. 2 species column (Douglas fir-larch, hem-fir, Southern pine, spruce-pine-fir), so no species picker is needed. Southern-Pine-only jurisdictions use a separate reduced-value table.
Header & studs
Code edition, lateral bracing, and wind level for the king-stud count.
Uncheck if cripple studs bear directly on the header — IRC footnote (f) then cuts the span of 2×8/2×10/2×12 headers by 30%.
Header span table — 24-ft building, exterior wall
Maximum header span (ft-in) and required jack studs by size, per IRC Table R602.7(1) — combined No. 2 species, 30 psf ground snow, roof and ceiling only (top floor / one story). Change the building width, snow load, or support above to see other columns.
| Header size | Max span | Jack studs / end |
|---|---|---|
| 1-ply 2×6 | 3'-1" | 2 |
| 1-ply 2×8 | 3'-11" | 2 |
| 1-ply 2×10 | 4'-8" | 2 |
| 1-ply 2×12 | 5'-5" | 2 |
| 2-ply 2×4 | 3'-1" | 1 |
| 2-ply 2×6 | 4'-7" | 1 |
| 2-ply 2×8 | 5'-9" | 1 |
| 2-ply 2×10 | 6'-10" | 2 |
| 2-ply 2×12 | 8'-1" | 2 |
| 3-ply 2×8 | 7'-3" | 1 |
| 3-ply 2×10 | 8'-7" | 1 |
| 3-ply 2×12 | 10'-1" | 2 |
| 4-ply 2×8 | 8'-4" | 1 |
| 4-ply 2×10 | 9'-11" | 1 |
| 4-ply 2×12 | 11'-8" | 1 |
King (full-height) studs are separate and come from Table R602.7.5 by span and wind. Where the table lists one jack stud, an approved framing anchor may replace it. Verify your locally adopted IRC edition.
Calculation Formulas
The maximum header span is read directly from the IRC prescriptive table, indexed by building width (measured perpendicular to the ridge) and the built-up header size and ply. Values are not calculated — they are transcribed from the code table.
Example:
24-ft building, 2-ply 2×10, roof + ceiling, 30 psf snow → 6'-10" maximum span.
For a given rough-opening width, the calculator walks the sizes from fewest plies and shallowest depth upward and returns the first whose tabulated span covers the opening.
Example:
A 6-ft opening in a 24-ft building needs a 2-ply 2×10 (6'-10" allowed).
The number of jack studs supporting each end of the header is a value published in the header table (the NJ column) — it is read, not computed. Where NJ equals one, an approved framing anchor to the full-height stud may replace the jack.
Example:
2-ply 2×10 at a 24-ft width → 2 jack studs each end (4 total).
Full-height studs at each end come from a separate table indexed by header span and wind speed/exposure — one up to an 8-ft span, two at 10–14 ft, three or four above in high wind.
Example:
A 6-ft header at ≤115 mph → 1 king stud each end; the same header in high wind → 2.
When the top of the header is not laterally braced — for example cripple studs bearing directly on it — the tabulated span for 2×8, 2×10 and 2×12 headers is reduced by 30 percent. Braced (sheathed) headers use the full value.
Example:
A 2-ply 2×10 at 12-ft width: 9'-0" braced → 6'-4" unbraced.
Each 2× member is cut to the rough-opening width plus the jack-stud bearing at each side, then rounded up to the next even foot of stock. The header is laminated from the required number of plies.
Example:
A 6-ft opening → cut roughly 6'-3", buy 8-ft 2× stock.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Species basis | Combined No. 2 (DF-L / HF / SP / SPF) | The IRC header table uses a single governing No. 2 column for all four species groups — no species selection is needed. Southern-Pine-only jurisdictions use a separate reduced-value supplement. |
| Building widths | 12 / 24 / 36 ft | The 2018 and 2021 IRC header tables are keyed to these widths (a change from the 2015 IRC's 20/28/36). Interpolation between widths is permitted. |
| Snow columns | 30 / 50 / 70 psf | The table gives three ground-snow columns; use 30 psf where ground snow is ≤30 psf and roof live load ≤20 psf. Interpolation between listed snow loads is permitted. All three are covered. |
| Footnote (f) factor | ×0.70 unbraced | Tabulated spans for 2×8/2×10/2×12 are multiplied by 0.70 where the header top is not laterally braced (cripples bearing on the header). |
| Bearing length | 1½" minimum each end | Minimum header bearing at each end on the jack stud(s), per R602.7 / R502.5. |
| Ply fastening | 2 rows 10d @ 16" o.c. | Built-up plies are nailed with two rows of 10d nails at 16 inches on center along each edge; a 2-ply header in a 2×4 wall adds a ½" plywood spacer. |
| King-stud nailing | Four 16d nails | The full-height (king) stud adjacent to each header end is end-nailed to the header with four 16d nails (R602.7.5). |
| Framing-anchor option | NJ = 1 only | Where the table requires a single jack stud, an approved framing anchor attached to the full-height stud may support the header end in place of the jack. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
IRC Table R602.7(1) — Exterior Header & Girder Spans(IRC R602.7 / Table R602.7(1))
View StandardThe prescriptive span table for headers and girders in exterior bearing walls. Gives the maximum span and required jack studs by building width, ground snow load, supported load, and built-up header size — for a single combined No. 2 species column.
Key Requirements:
- •Span and jack-stud count read from the table by width and header size
- •Building widths 12/24/36 ft (2018/2021); interpolation permitted
- •Combined No. 2 species — DF-L, hem-fir, Southern pine, spruce-pine-fir
- •Footnote (f): reduce 2×8/2×10/2×12 spans by 0.70 when the header top is unbraced
IRC Table R602.7(2) — Interior Header & Girder Spans(IRC R602.7 / Table R602.7(2))
View StandardThe companion prescriptive table for interior bearing walls, indexed by building width and the number of floors supported (one or two floors — no snow/roof case). Fully covered by this calculator.
Key Requirements:
- •Span and jack-stud count by building width and floors supported
- •One-floor and two-floor supported conditions
- •Same combined No. 2 species basis
- •Same 0.70 lateral-bracing footnote for 2×8/2×10/2×12 headers
IRC R602.7.5 — Full-Height (King) Studs(IRC Table R602.7.5)
View StandardSets the minimum number of full-height studs at each end of a header as a function of header span and wind speed/exposure, independent of the jack-stud count.
Key Requirements:
- •One king stud each end up to an 8-ft header span
- •Two king studs each end at 10–14 ft
- •Three or four king studs each end above 14 ft in high wind
- •End-nail each king to the header with four 16d nails
IRC R602.7.1 / R602.7.3 — Header Assembly(IRC R602.7.1, R602.7.3)
View StandardDetails for single-member and built-up headers, spacers, and the restraint of wide headers spanning large openings.
Key Requirements:
- •Built-up plies nailed per Table R602.3(1); ½" spacer to fill a 2×4 wall
- •Single-ply headers get a flat 2× top and bottom plate nailed at 12" o.c.
- •Wide headers over long spans must be restrained at the wall top or sheathed
- •Minimum 1½" bearing at each end
AWC Wood Frame Construction Manual (WFCM)(AWC WFCM)
View StandardThe American Wood Council manual the IRC wall provisions draw from. It provides the engineering basis for the prescriptive header tables and extended span tables for cases the IRC does not tabulate.
Key Requirements:
- •Design basis for the IRC header/girder tables
- •Combined No. 2 species design values
- •Extended tables for widths and loads beyond the IRC grid
- •Engineered alternative when the prescriptive table is exceeded
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Code Edition
2015 vs. 2018/2021
The header table's building-width axis changed between editions — the 2015 IRC used 20/28/36 ft, while the 2018 and 2021 IRC use 12/24/36 ft. The 2018 edition also added footnote (f), the 0.70 reduction for unbraced headers. The 2024 IRC expands to widths of 20/24/28/32/36/40 ft.
Regional Examples:
Ground Snow Load
30 vs. 50+ psf
Header spans shrink as ground snow load rises. The table publishes 30, 50, and 70 psf columns; use the 30 psf column only where ground snow is 30 psf or less and roof live load is 20 psf or less. Interpolation between listed snow loads is permitted.
Regional Examples:
Wind & Exposure
King-stud count
The number of full-height (king) studs at each end tracks wind speed and exposure category. A coastal or open-terrain site in a high-wind zone requires more king studs — and heavier uplift connections — than an inland site in Exposure B.
Regional Examples:
Southern Pine Jurisdictions
2013 design-value reduction
A 2013 revision cut visually-graded No. 2 Southern Pine design values by roughly 25–30 percent. Some jurisdictions (and the combined table in older editions) are non-conservative for Southern-Pine-only framing, so states like North Carolina publish a separate Southern-Pine header supplement.
Regional Examples:
Beyond the Prescriptive Table
When you need an engineered beam
Openings wider than the largest tabulated span for a size, headers carrying point loads or beams, and interior girders past the table all fall outside the prescriptive code. These require an engineered solution — commonly an LVL, LSL, glulam, or steel beam sized by the manufacturer or an engineer.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
Plan disposal before you start
Smaller jobs still produce more debris than a few trash bags can hold. Check what's allowed in a dumpster and which disposal option fits the scope.
See disposal options →
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How to Use This Calculator
- Choose a mode: find the header for an opening you know, or the widest opening a header size can carry.
- Pick the wall type and building width, and (for an exterior wall) your ground snow load and what the header supports.
- Set the code edition and your wind exposure — the wind level sets the king-stud count.
- Enter the rough-opening width (or select the header size you have).
- Leave "header top laterally braced" checked unless cripple studs bear directly on the header, which triggers the footnote-(f) reduction.
- Click Calculate for the header size and ply, jack and king stud counts, the framing take-off, and other sizes that also work.
How the IRC Sizes a Header
A header is a small beam over an opening, and the IRC sizes it prescriptively from two things: how wide the building is (which sets how much floor and roof load funnels to the wall) and what the header carries. The wider the building and the more floors above, the shorter a given header can span — so a 2-ply 2×10 that reaches 9 feet in a 12-foot-wide building drops to about 5 feet in a 36-foot-wide building. The number of jack (trimmer) studs at each end is printed right in the table; where it calls for one jack, an approved framing anchor to the full-height stud may replace it. King studs are separate — Table R602.7.5 sets them by header span and wind, from one on a short opening up to three or four on a wide header in a high-wind zone. One rule catches people: if the top of the header is not braced by sheathing or perpendicular framing — cripple studs sitting directly on it — you have to multiply the tabulated span of a 2×8, 2×10, or 2×12 by 0.70. Sheathe the header top and you get the full span back. When even a 4-ply 2×12 will not reach your opening, the prescriptive table is exhausted and you need an engineered beam — an LVL, LSL, glulam, or steel — sized by the manufacturer or an engineer.
Frequently Asked Questions
What size header do I need for a window or door?
It depends on the opening width, how wide your building is, and what the header carries. Per IRC Table R602.7(1) for a roof-and-ceiling load at 30 psf snow, a 2-ply 2×8 covers roughly a 4- to 6-foot opening depending on building width, a 2-ply 2×10 reaches about 5 to 9 feet, and a 2-ply 2×12 or a 3-ply gets you into wider openings. Enter your numbers and this calculator returns the smallest built-up header that spans the opening, plus the jack and king studs each end. A wider building funnels more load to the wall, so the same header spans less.
What's the difference between jack studs and king studs?
Jack (trimmer) studs are the cut studs under each end of the header that carry its load down to the plate — their count comes straight from the NJ column of IRC Table R602.7(1). King (full-height) studs run continuously from the bottom plate to the top plate alongside the jacks and resist racking and wind; their count comes from a separate table, R602.7.5, based on the header span and wind exposure. A typical small opening has one jack and one king each end; a wide header in a high-wind zone can need two or three of each. This calculator reports both.
Do I need a header in a non-load-bearing wall?
Structurally, no — a wall that carries no load above the opening does not need a sized structural header; a flat 2× or a single stud on the flat is enough to nail off the drywall and hold the cripples. But confirm the wall is truly non-bearing before you skip the header: interior walls running perpendicular to the joists, or under a girder or bearing point, often carry load even when they look like partitions. This calculator sizes headers for bearing walls; use it whenever the wall carries a roof, ceiling, or floor above.
Can I use a single 2×10 instead of a double?
You can look it up — IRC Table R602.7(1) does list single-ply (1-2×) headers — but a single member is rarely the right call for a bearing wall: its spans are short and it leaves a hollow wall cavity. For most door and window openings you'll laminate two plies (with a ½-inch plywood spacer to fill a 2×4 wall) or three plies in a 2×6 wall. This calculator's 'find my header' picks a built-up 2-, 3-, or 4-ply header, but you can select a single-ply size in 'max opening' mode to see its tabulated span.
Does snow load change the header size?
Yes. Heavier roof loads shorten how far a header can span, so the IRC table has separate columns for ground snow load — 30, 50, and 70 psf — all three of which this calculator covers. Use the 30 psf column only where your ground snow load is 30 psf or less and the roof live load is 20 psf or less; above that, pick 50 or 70 psf and you'll typically need a deeper header or more plies for the same opening. Interpolation between the listed snow loads is permitted by the code.
What does 'header top not laterally braced' mean, and why does it cut the span?
IRC footnote (f) reduces the tabulated span of a 2×8, 2×10, or 2×12 header by 30 percent (multiply by 0.70) when the top of the header isn't braced against sideways buckling — for example when cripple studs bear directly on it with no sheathing tying it off. A header sheathed with structural panel or braced by perpendicular framing gets the full tabulated span. Leave the calculator's bracing box checked for normal sheathed construction; uncheck it only when the header top is genuinely unbraced.
When do I need an engineered beam (LVL or steel) instead?
When your opening is wider than the largest header the prescriptive table lists for your building width and load, or when the header carries a concentrated load such as a beam or post bearing on it. At that point the IRC table is exhausted and you need an engineered member — an LVL, LSL, glulam, or steel beam — sized by the manufacturer's span tables or a structural engineer. This calculator tells you explicitly when you've hit that limit rather than guessing a size that isn't in the code.