Door Header Size Calculator

Frequently Asked Questions

What size header for a 3-foot door opening in a load-bearing wall?

A 3-foot opening (under 3.5 ft) with one floor above requires a doubled 2x6 header.

What header size for a 6-foot garage door opening?

A 6-foot opening (5 to 6.5 ft range) in a load-bearing wall with one floor above needs a doubled 2x10.

Do I need a header in a non-load-bearing wall?

Technically only a flat 2x4 or 2x6 on edge is needed. Most builders install a doubled 2x6 for consistency and future flexibility.

How long should a header be for a 36-inch rough opening?

Total header length = rough opening + 6 inches for bearing = 36 + 6 = 42 inches (3.5 ft). Cut two pieces of the recommended lumber size to this length.

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Estimates for informational purposes only.

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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

A header spans a rough opening (door or window) and transfers the load above around the opening to the jack studs on each side. The required header size depends on three factors: how wide the opening is, whether the wall carries load from the floor or roof above (load-bearing), and how many stories of load it must support.

This calculator uses a simplified prescriptive table approach consistent with IRC Table R602.7. For load-bearing walls the header size steps up as opening width increases; for non-load-bearing walls a 2x4 flat or 2x6 on edge is sufficient regardless of width.

Header Sizing Rules

Non-load-bearing walls: Any opening width - a 2x4 flat (laid on its wide face) or 2x6 on edge is acceptable. Many builders use a doubled 2x4 or 2x6 regardless for consistency.

Load-bearing, 1 floor above:

Up to 3.5 ft: doubled 2x6

3.5 to 5 ft: doubled 2x8

5 to 6.5 ft: doubled 2x10

6.5 to 8 ft: doubled 2x12

Over 8 ft: engineered beam (LVL or PSL) required

Load-bearing, 2 floors above:

Up to 3.5 ft: doubled 2x8

3.5 to 5 ft: doubled 2x10

5 to 6.5 ft: doubled 2x12

Over 6.5 ft: engineered beam required

Header Installation Details

A typical header assembly consists of two pieces of dimensional lumber with a 1/2-inch plywood spacer between them to match the 3.5-inch width of a 2x4 stud wall (or a 5.5-inch spacer for a 2x6 wall). The header rests on jack studs (trimmers) on each side, which are nailed to full-height king studs. A minimum bearing of 1.5 inches on each side is required.

Total header length = rough opening width + 3 inches per side (for bearing on jack studs) = opening + 6 inches. When ordering lumber, plan two pieces at the total header length.

FAQ

How do I know if a wall is load-bearing?

Load-bearing walls run perpendicular to floor joists, sit above a beam or wall in the floor below, or are exterior walls. A wall parallel to joists with nothing below it is usually non-load-bearing. When in doubt, consult a structural engineer.

Can I use LVL for any opening width?

Yes. LVL (laminated veneer lumber) is a common upgrade for wide openings. Its higher Fb (typically 2,600 psi) allows shallower members or longer spans than sawn lumber. LVL headers must be sized by the manufacturer's span tables or an engineer.

Do I always need doubled headers?

Yes in wood-framed walls. The doubled header matches the 3-inch thickness of a 2x4 stud wall (two 1.5-inch pieces). A plywood spacer fills the remaining 0.5 inch in standard 2x4 framing.

What is the difference between a king stud and a jack stud?

The king stud is the full-height stud next to the opening. The jack stud (trimmer) is a shorter stud nailed to the king stud that supports the underside of the header. Together they form the rough opening sides.

Door Header Size Calculator

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