Door Header Size Calculator

Estimated header size for a door opening. Verify with span tables.

Recommended header 2 × 6 (double)

Formula: rule-of-thumb lumber size by span

Step-by-step with your numbers:

1. Values used:

2. Opening span (door width ) = 1

4. Recommended header = 2 × 6 (double)

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A rough rule-of-thumb for door header size. ALWAYS verify with span tables a structural engineer.

The math behind it

As a rough starting point: up to 4 ft double 2×6, up to 5 ft double 2×8, up to 7 ft double 2×10, up to 8 ft double 2×12.

6 ft door → double 2 × 10.

Load-bearing?

This is for single-story bearing; multi-story and heavy loads need professional sizing.