Door Header Size Calculator: Beam Span and Lumber Sizing

Your details

The clear width of the door opening, measured between the trimmer studs.
ft
Enter any remaining inches beyond the whole feet above.
in
Whether the wall carries loads from floors or roof above. When in doubt, treat as load-bearing.
Standard exterior walls are often 2x6; interior walls are usually 2x4.
Recommended headerPrescriptive lumber header
2x4 doubled

Minimum header size from IRC R602.7 prescriptive tables for the entered conditions.

Actual header depth3.5in
Jack studs per side1
Rough opening width36in
Header depth (in)3.5
Jack studs per side1

Use a 2x4 doubled for this opening.

  • For a 36.0-inch rough opening under load-bearing (roof and ceiling only) conditions, use a 2x4 doubled.
  • Install 1 jack stud (trimmer stud) on each side to transfer the header load to the sole plate.
  • Always use at least one king stud on each side of the jack stud to tie the header assembly to the wall framing.
  • Header sizing is based on IRC Table R602.7 prescriptive tables for Spruce-Pine-Fir or Douglas Fir-Larch No. 2; other species or grades may allow different spans.

Next stepVerify with your local building department - local amendments, snow loads, or seismic zones may require a larger header.

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