Select a header size from the drop-down menu to view its typical actual (dressed) dimensions. This tool does not determine a safe maximum span or provide structural header sizing—use local code span tables or a qualified engineer for load-bearing openings.

Door Header Size (Actual Dimension) Calculator

Door Header Size (Nominal vs Actual)

The following table shows typical actual (dressed) dimensions for nominal 4× lumber sizes commonly used as solid-sawn members. These are dimensions (size) only—not maximum spans. Actual sizes can vary by standard and moisture condition.

Nominal SizeTypical Actual Size (in)
4×43.5 × 3.5
4×63.5 × 5.5
4×83.5 × 7.25
4×103.5 × 9.25
4×123.5 × 11.25

What is a door header?

A door header is a structural member (often wood, engineered wood such as LVL, or steel) installed above a door opening to support loads above and transfer them to the framing at each side of the opening (such as jack studs or posts).

How big should the door header be?

The required header size depends on the opening width and the loads it supports (for example: roof/floor loads, number of stories, tributary width, snow load), as well as material species/grade and bearing details. For load-bearing openings, use your local building code header span tables or an engineered design. For non-load-bearing interior partitions, a header may be sized primarily for framing/attachment rather than structural capacity, per local practice/code.

How to calculate door header size?

To size a door header structurally, determine (1) the rough opening width, (2) whether the wall is load-bearing, and (3) what loads the header supports (roof, floor(s), snow, etc.).

Then select a header size from the applicable building-code span table (or from an engineered design). In many residential applications, headers are built-up members (for example, multiple 2× members or LVL) rather than a single 4× member.