Door Header Size Calculator
Determine the correct header size for any door or window opening. Select your span, whether the wall is load-bearing, and lumber species — get the minimum header depth per IRC Table R602.7, from doubled 2×4s for short spans to LVL beams for wide openings.
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.