Door Header Size Calculator

Determine the required header depth for doors and windows based on opening width and load conditions.

Structural Inputs

Unit System

Opening Width (in)

Load Condition

Assumes standard No. 2 grade lumber and normal residential loading.

Sizing Recommendation

Designing an opening?

Enter your door or window width and load type to see the minimum safe header dimensions.

Overview

Headers are horizontal structural beams that carry loads across door or window openings. Sizing is governed by the 'span' and the weight it must support (dead and live loads). For residential framing, this typically involves 2-ply dimensional lumber like 2x10s or 2x12s, depending on building code requirements for the specific load path.

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Pro Tips

Ensure you have at least one 'King Stud' and one 'Jack Stud' on each side of any opening up to 5 feet.
For exterior walls, sandwich a layer of 1/2-inch plywood or rigid insulation between two 2x header members to match the 3.5-inch wall depth.
Check with local codes if you are in a high-snow load area, as header requirements may be stricter.

Fun Facts

"Standard residential headers are usually 'jacked'—supported by shorter studs on each side of the opening."
"Nominal 2x4 lumber actually measures 1.5 x 3.5 inches (38 x 89 mm)."
"Engineered lumber like LVL (Laminated Veneer Lumber) can carry significantly higher loads than standard dimensional pine or fir."

Formula: As a rule of thumb, use (Span in ft + 2) inches of depth (e.g., 4ft span needs 6in depth, aka 2x6).

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