Door Header Size Calculator - IRC Table R602.7 Framing Sizes
Find the required header size, ply count, and jack/king stud count for a door or window opening based on rough opening width, wall bearing type, floors above, and ground snow load, following IRC Table R602.7. Cross-check the finished opening with our framing calculator before ordering lumber.
🏗 Door Header Size Calculator
Opening Width + Wall Type + Load Above + Snow Load → Header Size + Studs
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View Chart →How This Calculator Sizes Your Header
The calculator adds your rough opening allowance to the door or window width, then looks up that span against IRC Table R602.7 for the wall condition you select: bearing or non-bearing, and roof only, roof plus one floor, or roof plus two floors above [1].
Ground snow load above 30 psf shifts the lookup to a heavier load category, since additional snow load increases the total roof dead and live load the header must transfer to the jack studs [2]. Building width matters because wider buildings mean longer roof truss spans, which increase the load per linear foot carried by the header.
Header Span Ranges by Load Condition
These ranges summarize IRC Table R602.7 for buildings 28 feet wide or less, ground snow load 30 psf or less, No. 2 SPF or better lumber [1][2]. Wider buildings or higher snow loads require stepping up to the next header size.
| Header Span | Roof Only | Roof + 1 Floor | Roof + 2 Floors |
|---|---|---|---|
| Up to 3 ft 6 in | (2) 2x4 | (2) 2x6 | (2) 2x8 |
| 3 ft 6 in - 5 ft | (2) 2x6 | (2) 2x8 | (2) 2x10 |
| 5 ft - 7 ft | (2) 2x8 | (2) 2x10 | (3) 2x10 |
| 7 ft - 8 ft | (2) 2x10 | (3) 2x10 | (3) 2x12 |
| 8 ft - 10 ft | (3) 2x10 | (3) 2x12 | Engineered LVL required |
| 10 ft - 12 ft | (3) 2x12 | Engineered LVL required | Engineered LVL required |
Why Header Size Depends on More Than Just Width
A header carries the load from above straight down to the jack studs on each side of the opening. That load comes from whatever sits above the wall: roof framing alone, or roof plus one or more floors of framing, furniture, and occupants [1].
Building width changes the roof truss span, and longer trusses deliver more load per linear foot to every bearing wall below them, including the header. That is why IRC Table R602.7 is organized around both span and building width, not span alone [1].
Jack Studs and King Studs
Jack studs, also called trimmers, sit directly under each end of the header and carry the header load down to the sole plate and foundation. King studs run full height alongside the jacks and tie the header assembly into the top and bottom plates of the wall.
As spans grow, code requires more jack studs per side to spread the header's end reaction over more bearing area. A 3 foot opening typically needs one jack per side; an 8 foot opening typically needs two or three [3]. For heavier openings, cross-check the resulting reaction against our beam load calculator.
Step-by-Step: Sizing a Header for a 36 Inch Exterior Door
🏗 Step 1: Find the Rough Opening
Door width = 36 in, Rough opening add-on = 2 in
The header span always uses the rough opening, not the door slab width.
🏗 Step 2: Identify Wall Condition
Bearing wall, roof only above, building width = 28 ft, snow load = 30 psf
A single-story ranch home with this wall configuration is the most common residential case.
🏗 Step 3: Look Up Header Size
3 ft 2 in span, roof-only load, 28 ft building
This matches the common field rule that a double 2x6 handles most single exterior doors in single-story construction [2][3].
Mistakes That Lead to an Undersized Header
⚠ Using Door Width Instead of Rough Opening
The header must span the full rough opening, roughly 2 to 2.5 inches wider than the door itself. Sizing off the door width alone can leave the header too short for the actual framed opening [4].
💡 Accounting for Floors Above
A header sized correctly for roof-only load will be undersized if a second story is added later. Always confirm what is actually built above the wall, not just what is planned [1].
⚠ Ignoring Higher Snow Load Zones
IRC Table R602.7 default spans assume 30 psf ground snow load or less. Many mountain and northern regions exceed this, which requires stepping up to the next header size or consulting a structural engineer [2].
💡 Skipping the King Stud
King studs are not optional filler; they tie the header assembly into the top plate and resist racking. Skipping them, even on short spans, is a common framing inspection failure.
Ordering Lumber for the Header Assembly
Built-up headers use two or three plies of dimensional lumber nailed or bolted together, with a strip of half-inch plywood sandwiched between plies on 2x lumber to bring the header flush with a standard 2x4 wall. Order full-length stock; splicing header plies mid-span is not permitted under most residential codes [3].
For spans beyond what dimensional lumber allows, order engineered LVL or PSL headers sized by a structural engineer or the manufacturer's span tables, and confirm bearing length requirements with your local building department before framing. Track total board footage with our board foot calculator and estimate the full stud package with our lumber calculator.
Frequently Asked Questions
A 36 inch door has a rough opening of about 38 inches. For a single-story bearing wall with roof load only, a double 2x6 header is typically sufficient per IRC Table R602.7. Non-bearing walls can use a double 2x4.
Bearing walls carry roof and floor loads down to the foundation, so their headers are sized from IRC Table R602.7 based on span, building width, and snow load. Non-bearing walls, usually parallel to floor joists, only support their own weight, so a minimum double 2x4 header is generally allowed per code.
IRC framing practice generally calls for 1 jack stud per side for spans up to 4 feet, 2 jack studs per side for 4 to 8 foot spans, and 3 jack studs per side for spans over 8 feet, with 1 king stud per side in most residential framing.
Yes. IRC Table R602.7 header spans are published for a ground snow load of up to 30 psf. Higher snow loads increase roof dead and live load, which can require a larger header or engineered lumber even at the same span.
Dimensional lumber headers from IRC Table R602.7 typically max out around 8 to 12 feet depending on load condition. Beyond that span, or for heavy point loads, an engineered LVL or PSL header sized by a structural engineer is required.
The rough opening is typically 2 to 2.5 inches wider than the nominal door width to allow for jamb material and shim space. A 36 inch door commonly needs a 38 inch rough opening, which is the dimension used to size the header span.
A single flat 2x4 header is allowed by code for openings up to about 8 feet wide in non-bearing walls only. For bearing walls, doubled dimensional lumber sized per IRC Table R602.7 is required.
Sources and Methodology
Last reviewed: July 2026.
- [1] IRC Table R602.7, "Girder and Header Spans for Exterior and Interior Bearing Walls," as summarized in Jaspector, IRC 2024 Header Sizing R602.7.
- [2] Snow load and building width adjustments to header span category, per IRC Table R602.7 notes, as summarized in ProjectCalc, Door and Window Header Sizes IRC Quick-Pick.
- [3] Jack stud and king stud count conventions for residential framing, consistent with standard IRC wall framing practice and multiple published span quick-reference guides.
- [4] Rough opening allowance conventions (2 to 2.5 inches over nominal door width) per standard door manufacturer installation instructions and framing trade practice.
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