Door Header Size Calculator
Header sizing depends on span, load, lumber species, and whether the wall is load-bearing -- there is no single formula, only span tables that vary by jurisdiction. The calculator below currently helps you work out stud layout around the opening. For the header beam size itself, use the reference tables further down this page as a starting point, then confirm against your local building code's span tables (e.g. IRC Table R602.7) or a structural engineer before framing any load-bearing opening.
Door Header Size by Opening Width — Quick Reference
IRC Table R602.7 provides prescriptive header sizes for load-bearing walls in residential construction. For Douglas Fir-Larch #2 lumber supporting one floor and roof (20 psf live load on roof, 10 psf dead load, 40 psf live load on floor):
- Up to 4 ft: doubled 2×6
- 4 to 5 ft: doubled 2×8
- 5 to 6 ft: doubled 2×10
- 6 to 8 ft: doubled 2×12
- 8 to 10 ft: 3-ply 2×12 or LVL equivalent
- 10 to 12 ft: engineered LVL or steel — consult engineer
These are minimums. Always size up one grade for safety or when loads are uncertain. In non-load-bearing walls, use a doubled 2×4 or 2×6 for any opening under 8 ft.
How to Size a Door Header: Variables That Matter
Four variables determine correct header size: span, load, lumber species, and support conditions. Span is the rough opening width (not the door size — add 2–3 inches for framing). Load depends on what's above: ceiling only, one floor + roof, or two floors + roof each require progressively larger headers.
Lumber species matters more than most contractors realize. A header that works in Douglas Fir-Larch might be undersized in Hem-Fir or SPF (Spruce-Pine-Fir), which have lower fiber bending strength. The IRC span tables specify species groups — confirm what's being used at the lumberyard.
Support conditions also matter. A header in a fully sheathed wall has different lateral support than one in an open framed wall. And point loads from posts, beams, or ridge connections above a header can add significant concentrated force — these require engineered calculations, not just prescriptive tables.
LVL Headers vs. Dimensional Lumber Headers
Laminated Veneer Lumber (LVL) headers are the industry standard for openings over 6 feet. LVL is stronger per inch of depth than solid dimensional lumber, stays straight over time, and comes in longer lengths. Typical LVL header sizes are 1.75×9.25 in, 1.75×11.25 in, and 1.75×14 in — doubled or tripled based on load.
Cost comparison: doubled 2×12 Douglas Fir header costs roughly $40–60 for an 8-ft span. A 3.5×11.25 LVL costs $80–120 for the same span but carries much more load and eliminates crown/warp callbacks. For any opening over 8 ft or any situation with significant load uncertainty, the LVL premium pays for itself in callbacks avoided.
Frequently Asked Questions
What size header do I need for a 3-foot door?
A standard 3-ft (36-in) door rough opening of about 38 inches typically requires a doubled 2×4 (for non-load-bearing walls) or a doubled 2×6 header (for load-bearing walls in single-story construction). In two-story buildings or with heavy loads above, use a doubled 2×8 or 2×10. Always verify against your local code's span tables.
What is the formula for sizing a door header?
Headers are sized from span tables, not a single formula. The key variables are: clear span (rough opening width), tributary load width (how much roof/floor load bears down), lumber species and grade, and whether the wall is load-bearing. IRC Table R602.7 provides prescriptive header sizes for residential construction up to 40 psf roof load.
What size header for a 6-foot opening?
A 6-ft (72-in) rough opening in a load-bearing wall under a single story typically requires a doubled 2×10 or 4×10 header in Douglas Fir-Larch. Under a two-story load, you may need a doubled 2×12 or an engineered LVL beam. For non-load-bearing walls, a doubled 2×6 is usually sufficient for 6-ft spans.
Can I use a single piece of lumber for a door header?
Single solid lumber headers (4× stock) work but are less common than doubled 2× headers with a plywood spacer. Engineered lumber (LVL, PSL) is preferred for wide openings above 6 ft because it's straighter, stronger, and won't crown or twist after installation. For structural headers in load-bearing walls, always use lumber rated for beam/header use.
Does a garage door header need to be larger than a standard door header?
Yes, significantly. A standard single garage door (9 ft wide) needs a much deeper header than an interior door. Expect a doubled 2×12, 3-ply 2×12, or LVL beam for a 9-ft opening with a floor above. A 16-ft double garage door typically requires a steel beam or multi-ply LVL engineered for the specific load — always get an engineer's stamp for garage openings over 10 ft.