Door Header Size Calculator

Door Header Size Calculator works out, in seconds, the wood header (lintel) you need over a door, window or garage opening in a framed bearing wall. Enter the opening width, what the wall carries above, your building width and ground snow load, and read the required built-up header — for example 2-2x8 or 2-2x10 — along with the jack studs, king studs and bearing. It works completely offline and nothing you enter ever leaves your phone.

HOW IT WORKS
The app follows the IRC prescriptive header tables:

1. It takes your rough opening width — the clear span the header must cross.

2. You tell it what is stacked above the opening: roof and ceiling only, or roof and ceiling plus one or two floors. A header that also carries a floor must be deeper than one carrying roof alone.

3. The building width (20, 28 or 36 ft) and the ground snow load (30, 50 or 70 psf) set how much tributary roof and floor load drains onto the header. The app rounds each up to the next table step.

4. It then picks the shallowest built-up header of your chosen build-up (two 2x boards for a 2x4 wall, three for a 2x6 wall) whose tabulated maximum span covers your opening, and reads off the required number of jack (trimmer) studs.

The numbers come from IRC Table R602.7(1), Girder Spans and Header Spans for Exterior Bearing Walls, for No. 2 grade Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir.

WHAT YOU CAN DO
- Enter an opening in feet and inches and read the required header instantly
- Choose the load carried above: roof and ceiling, plus one or two floors
- Set your building width and ground snow load
- Switch between a 2-ply header for 2x4 walls and a 3-ply header for 2x6 walls
- See jack studs, king studs, bearing length, cripple studs and the built-up thickness
- Open Details for a step-by-step breakdown and the IRC span table for every header size at your load
- Learn how a header carries load and why the size changes, in plain language

BUILT FOR CLARITY
A warm, iron-oxide design puts the required header first, with the supporting figures right beside it. Light and dark themes, a tiny download, no clutter and no account required.

AN ESTIMATE, NOT AN ENGINEERED DESIGN
This is an educational tool on the IRC prescriptive path at the stated loads and lumber species. A header holds up the wall and roof over the opening: if it is undersized it can sag or fail. It is NOT a substitute for a licensed structural engineer. Interior bearing walls use a different table (R602.7(2)), and garage doors, long spans and any loads beyond the tables must be sized by an engineer with an engineered beam such as LVL, glulam or steel. Always confirm the design against your adopted local code and have it reviewed before you build.

PRIVACY
The app collects no personal data and works fully offline. Ads are served by Google AdMob, which may use an advertising identifier as described in Google's policies.

Download Door Header Size Calculator and get a quick, sensible starting point for the header over your next opening.

Recent changes:
improve app performance