Door Header Size Calculator — IRC Residential Sizing
Enter the rough opening span and whether the wall is load-bearing to get the minimum header lumber size required by the International Residential Code (IRC 2021) for single-storey residential construction.
Wall type
Opening span unit
ft
How does this calculator work?
Look up your rough opening span in IRC 2021 Table R602.7 for the wall type (bearing or non-bearing). For a bearing wall up to 3.5 ft use 2×4 doubled; up to 5 ft use 2×6; up to 6.5 ft use 2×8; up to 8 ft use 2×10; up to 9.5 ft use 2×12; wider spans need engineered lumber. Values assume Douglas Fir-Larch No. 2, single-storey residential.
Formula
How this is calculated
A door or window header is the horizontal beam across the top of the rough opening that carries the load from above and distributes it to the trimmers (jack studs) on each side. In bearing walls — walls that support the floor, roof, or another storey — the header must be sized to carry significant loads; in non-bearing partition walls it is mainly structural filler and much smaller sizes work.
This calculator uses the prescriptive span table from IRC 2021 Section R602.7 (Table R602.7), which lists the minimum header sizes for 2× Douglas Fir-Larch No. 2 lumber (two members doubled with a ½" plywood spacer to match a 3½" stud wall) for a ground-floor bearing wall supporting one storey above plus a roof. The table selects the smallest nominal size whose span limit exceeds your opening width. Openings beyond 9.5 ft in bearing walls typically require a 3×12 LVL or a custom-engineered beam.
These values are a guide for light-frame residential construction under the IRC. Real-world sizing depends on local amendments to the code, lumber species and grade, actual loads (snow, wind, multi-storey), header support conditions, and inspection by a licensed professional. Always confirm the selection with your local building department and a structural engineer for anything beyond a simple one-storey residential opening.
Frequently asked questions
A bearing wall carries live and dead loads from above (floor joists, roof rafters, or another storey). Its header must be engineered to transfer that load to the foundation. A non-bearing partition wall supports only its own weight, so the header is essentially decorative blocking and a much smaller size is adequate.
For simple ground-floor openings up to about 8–10 ft in a single-storey home, the IRC prescriptive table is usually sufficient and a permit is obtained without an engineer's stamp. For larger spans, multi-storey loads, or any unusual conditions (concentrated point loads, hip or valley rafter bearing, etc.), hire a licensed structural engineer.
The table uses Douglas Fir-Larch No. 2 — one of the most common framing species in North America. If you are using Southern Yellow Pine, Hem-Fir, or Spruce-Pine-Fir, span allowances differ. Check the IRC appendix or consult a local engineer.
TG we-Calculate Editorial Team. (2026). Door Header Size Calculator — IRC Residential Sizing [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/door-header-size-calculator
TG we-Calculate Editorial Team. "Door Header Size Calculator — IRC Residential Sizing." TG we-Calculate. 2026. https://we-calculate.com/calculator/door-header-size-calculator.
TG we-Calculate Editorial Team, "Door Header Size Calculator — IRC Residential Sizing," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/door-header-size-calculator
@misc{wecalculate_door_header_size_calculator, title = {Door Header Size Calculator — IRC Residential Sizing}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/door-header-size-calculator}}, year = {2026}, note = {TG we-Calculate} }
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