Header Size Calculator

Estimate header load, header size, bending stress, shear stress, deflection, support reactions, and simplified utilization for door, window, garage, wall, and beam openings. Use this header size calculator for wood headers, LVL headers, built-up headers, and preliminary structural planning.

Calculate Header Size

Header line load = area load × tributary width + wall load + self weight. Header checks use M = wL² ÷ 8 and deflection = 5wL⁴ ÷ 384EI.
Your result will appear here.

How the header size calculator works

Load conversion:
The calculator converts dead, live, roof, or snow load into a line load using tributary width, then adds wall load and header self weight.

Header section:
The calculator uses ply width, number of plies, and depth to estimate area, section modulus, and moment of inertia.

Strength checks:
The calculator estimates bending stress and shear stress, then compares them to the entered allowable design values.

Deflection check:
The calculator estimates header deflection and compares it to the selected span limit.

Why use a header size calculator?

A header size calculator helps estimate whether a header size may be reasonable for a window, door, garage, wall, or beam opening.

It can help compare opening span, tributary load, plies, header depth, line load, bending, shear, deflection, support reactions, and simplified utilization.

What your result means

Your result shows estimated header size, line load, total load, reactions at each end, maximum moment, bending stress, shear stress, deflection, allowable deflection, and utilization percentages. These are simplified planning estimates only.

Header size formulas

Frequently asked questions

What is a header?

A header is a horizontal structural member above an opening that transfers load around the opening to supports, jack studs, posts, or walls.

How do you estimate header load?

Multiply the area load in PSF by the tributary width carried by the header, then add wall load, header self weight, and any point loads.

What size header do I need?

The required header size depends on span, loads, material, number of plies, bearing, deflection limits, and local code. This calculator gives a simplified planning check, not final design.

Can this replace span tables or engineering?

No. Final header sizing should use approved code span tables, engineered lumber product data, steel tables, local code requirements, connection details, bearing checks, and professional review when needed.