🚪 Door Header Size Calculator
Get a general estimate of the built-up header size typically used for a given door or window rough opening span.
What This Calculator Does
This tool gives a general, simplified estimate of the built-up dimensional lumber header size commonly used to span a door or window rough opening, adjusted for how much load the header carries above it.
The Method
A widely used rule of thumb for quick estimating is that header depth in inches is roughly 2 × the span in feet for a lightly loaded wall, scaled up for heavier load conditions such as a load-bearing wall supporting one or two additional stories. This mirrors the general shape of prescriptive header span tables found in residential building codes, which give minimum header sizes for common spans and loading conditions.
This is only a rough planning estimate, not an engineered design. Actual header requirements depend on species and grade of lumber, tributary load width, snow load, and local code tables (such as the IRC header span tables) or an engineer’s calculation — always verify final header size against your local building code or a structural professional before framing.