What size header do I need for a 3-foot door?

A doubled 2x6 or 2x8 is sufficient for a 3-foot interior or exterior door in most single-story applications. Consult span tables for multi-story or high-load situations.

How long should the header be?

Header length = rough opening width + 3 inches (for the two jack/trimmer studs at 1.5" each). This calculator adds 12 inches to allow proper bearing.

Header Calculator

Calculate the correct header length for door and window openings in your wall framing.

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Enter Your Measurements

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How to Use This Calculator

1Enter the rough opening width in feet.
2Enter the total number of openings.
3Click Calculate — get header lumber length, king studs, and jack studs.

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About This Material

Headers span door and window openings, transferring roof and floor loads around the opening to jack studs and king studs. Header size depends on span and load. Common sizes: 2x6 for small windows up to 4x12 for large openings.

Installation Tips

•Build headers from doubled 2x lumber with a 1/2" plywood spacer to match wall width.
•Or use LVL (laminated veneer lumber) for larger spans.
•Install with crown up.

Common Mistakes to Avoid

Undersizing headers for the span and load.
Not adding jack studs (trimmers) to support the header ends.
Forgetting the cripple studs above the header.