Article — Door Header Size Calculator
Door Header Size Calculator: IRC R602.7 Sizing Guide
A 3-foot door in a load-bearing wall with roof load only needs a (2) 2×4 header. The same door with a floor above needs (2) 2×6. With two floors above, (2) 2×8. The IRC R602.7 rule of thumb: header depth in inches equals twice the opening width in feet for ceiling-only loads. Heavy snow zones add 25 percent to the effective load. All headers are doubled members.
What is a door header?
A door header is a horizontal structural beam spanning the top of a door rough opening, transferring loads from above (floors, roof, snow) down through jack studs at each side of the opening. Without a properly sized header, the wall around the opening sags or fails under load.
Every door in a framed wall requires a header. Non-bearing interior partitions need only a minimal header — typically (2) 2×4s — to maintain wall alignment and provide trim nailing. Load-bearing walls (most exterior walls and some interior walls perpendicular to ceiling joists) require properly sized structural headers per IRC R602.7.
The door header size formula
The base rule for header depth: depth in inches must be at least twice the opening width in feet for ceiling-only loads. A 4-foot opening needs at least 8-inch deep header (2×8). A 6-foot opening needs 2×12. The rule extends naturally — every 2 inches of depth handles another foot of width under standard residential loads.
For floor loads above, multiply the effective span by 1.30. For two floors plus ceiling, multiply by 1.65. Heavy snow zones add 25 percent. Building width over 32 feet adds 10 percent because more roof load transfers to each linear foot of bearing wall. After all multipliers, round up to the next standard lumber size.
The IRC R602.7 header tables were developed in the 1970s based on light-frame construction research at USDA's Forest Products Laboratory. The tables specify minimum sizes that work conservatively across all common species and grades of lumber. Specialized engineering can sometimes use smaller headers in specific situations, but the tables remain the residential standard.
Door header IRC tables
The 2021 IRC publishes header span tables in chapter R602. The tables cover dimensional lumber from 2×4 through 2×12, doubled members for 2×4 walls and tripled for 2×6 walls. Spans run from 2 feet up to 16 feet depending on load combination.
For openings beyond the tables (over 12 feet in load-bearing walls), engineered lumber takes over. LVL (laminated veneer lumber) handles spans up to 24 feet with proper engineering. PSL and LSL products offer similar performance at slightly different price points. All engineered solutions require sealed engineering drawings for permit.
- 2×4 header = up to 4 ft (ceiling load)
- 2×6 header = up to 6 ft (ceiling)
- 2×8 header = up to 8 ft (ceiling)
- 2×10 header = up to 10 ft (ceiling)
- 2×12 header = up to 12 ft (ceiling)
- LVL = 12 to 24 ft (engineered)
Door header load types
Three standard load conditions cover most residential doors. Ceiling-only loads apply to single-story buildings or interior bearing walls with only roof load above. Floor-plus-ceiling loads apply when one floor and the roof load down through the wall. Two-floor-plus-ceiling loads apply to three-story walls bearing both upper floors.
Each load type increases the effective span the header must support. The 1.3 multiplier for one floor above accounts for the dead and live load of a typical residential floor (10 psf dead + 40 psf live). The 1.65 multiplier for two floors compounds that. These multipliers are conservative for typical bedroom and living spaces.
Door header snow load zones
Ground snow load varies dramatically across the US, from 0 psf in Florida to 100 psf in northern Maine, upper Michigan, and the Cascade Mountains. The IRC categorizes zones as light (0-30 psf), medium (30-50 psf), and heavy (50-70 psf). Above 70 psf typically requires engineered design.
Heavy snow zones add 25 percent to the header load. A 6-foot opening that would size as (2) 2×10 in Atlanta becomes (2) 2×12 in Vermont. The Federal Emergency Management Agency publishes county-level snow load maps that local building departments adopt. Always check the local ground snow load before sizing headers.
When in doubt, size up to the next lumber depth. A 2×10 instead of 2×8 adds about $4 to materials cost but provides significant safety margin and code reserve. Undersized headers are the most common framing inspection failure on residential rough-in.
Door header jack and king studs
Jack studs (also called trimmer studs) support the header at each side of the opening. They sit against the king studs and run from the bottom plate up to the header underside. King studs flank the jacks, running full wall height to provide lateral stability.
The number of jack studs scales with opening width and load. Up to 6-foot openings need 1 jack per side. Up to 8-foot openings need 2 jacks per side. Up to 12-foot openings need 3 jacks per side. Always use 2 king studs per side regardless of opening width — they provide racking resistance and trim nailing.
Engineered LVL door headers
LVL (laminated veneer lumber) is the engineered alternative to dimensional lumber for door headers spanning over 12 feet. Made from thin softwood veneers glued in parallel grain layers, LVL achieves bending strength roughly twice that of #2 SPF lumber at the same cross-section.
Standard LVL sizes for residential headers include 1.75" × 9.5", 1.75" × 11.875", 1.75" × 14", and 1.75" × 16". Multiple LVLs can be sistered together for higher loads. For garage door openings (16 to 24 feet wide), expect to use 1.75" × 14" LVL members, typically two or three sistered.
Door header mistakes
The first mistake is using a single header instead of doubled. Single headers lack the bearing capacity for any span over 2 feet and fail IRC inspection. Always sandwich two members with a 1/2-inch plywood spacer in 2×4 walls (totaling 3.5 inches wide to match wall thickness).
The second mistake is ignoring snow load. A house in Vermont needs heavier headers than identical framing in Tennessee. The third mistake is using lumber stamped for non-structural use (like utility-grade or stud-grade) as header material. Headers must be #2 or better visual grade dimensional lumber, or engineered LVL for spans over 12 feet.
Big box stores stock multiple grades of dimensional lumber. Headers require #2 or better — utility-grade and stud-grade lumber lacks the strength rating for structural use. Look for the grade stamp on every piece. Mixing grades in a doubled header (one #2 and one utility) creates an inspection failure.