Door Header Size Calculator

How Door Header Size Calculator Works?

The Door Header Size Calculator models the header as a simply supported beam spanning the clear door opening between the supporting wall or jack studs. It combines the load from the tributary floor or roof area with the wall line load to determine the uniform load acting along the header.

Here, $w$ is the total uniform header load, $b$ is the tributary width, $D$ is the dead load, $L$ is the live load, and $w$_wall is the wall line load. A concentrated load from a beam, girder, post, or truss is added separately at the specified position along the span.

For a span $L$ with a uniform load $w$, the basic support reactions are calculated from static equilibrium. If a concentrated load $Pis\; located\; a\; distance$ afrom\; the\; left\; support,\; the\; reactions\; are:$$

The calculator uses the resulting shear and bending behavior to determine the maximum bending moment and maximum shear. For the uniform-load component, the central-span bending moment is:

The concentrated load adds a position-dependent moment, so the governing moment is evaluated using its specified location rather than assuming it is centered. The selected header material supplies the allowable bending stress, shear capacity, modulus of elasticity, and bearing properties. For a rectangular header section, the main section properties are:

In these expressions, $b$ is header width and $d$ is header depth. Bending utilization compares the calculated bending stress with the material's allowable bending stress, while shear utilization compares calculated shear with allowable shear capacity. Deflection is calculated from the header stiffness, span, uniform load, and concentrated load, then compared with the selected span-to-deflection limit such as L/180, L/240, L/360, or L/480.

Bearing length is checked by dividing the support reaction by the allowable bearing pressure and available header width. The required header depth is the minimum depth that satisfies bending, shear, and deflection checks. The recommended nominal depth rounds that calculated requirement upward to a practical standard depth.

Practical Use Cases

Builders and framing contractors can enter the opening width, bearing length, tributary width, wall load, and material choice to compare practical header depths before framing a new door opening. The calculated reactions and bearing requirement also help identify whether the jack-stud arrangement provides sufficient support.

Structural engineers and designers can use the calculator as a preliminary screening tool for wood or LVL headers. The concentrated-load position is useful when a post, girder, truss, or beam bears directly on the header instead of loading it uniformly.

Remodeling contractors can estimate the effect of widening an existing door opening or changing the supported framing. Comparing bending, shear, and deflection utilization helps show which design criterion controls the required header depth.

Homeowners and owner-builders can use the results to understand how span, wall construction, floor or roof loading, material grade, and deflection criteria affect header size. The output can provide useful information for discussions with a qualified building professional before construction begins.

Building inspectors and project reviewers can use the reported reactions, bearing length, material selection, and utilization percentages as an organized preliminary check of the assumptions submitted for a door-opening design.

Accuracy and Limitations

The calculator provides a preliminary simply supported beam analysis using the entered span, tributary width, dead and live loads, wall line load, concentrated load, material properties, header width, and selected deflection limit. It assumes the supports are adequate, the header acts compositely as entered, loads are transferred vertically, and the header has no significant damage, holes, notches, lateral instability, torsional effects, or construction defects. It does not independently verify the supporting studs, foundation, load path, connections, fasteners, uplift, lateral loads, seismic or wind effects, irregular framing, multiple openings, or local building-code requirements. A concentrated load located outside the clear span or a header supporting unusual structural systems can make the simplified model unsuitable. Results should therefore be checked by a qualified structural professional and against the governing code before construction.

Quick Examples