Wood Header Span Calculator Guide
A wood header carries wall, floor, roof, or point loads over an opening. It transfers those forces to jack studs, posts, or other supports. Correct sizing helps limit cracking, sagging, and unsafe movement. This calculator gives a practical estimate for common rectangular wood headers.
What the calculator checks
The tool estimates uniform load from live, dead, snow, and roof inputs. It also lets you add line load and one centered point load. It then checks bending stress, shear stress, bearing demand, and deflection. Each check is compared with adjusted allowable values. The lowest safety ratio is shown as the controlling result.
Choosing inputs
Start with the clear opening span. Use the distance between inside bearing faces, not the total beam length. Add tributary width from the supported floor or roof area. Choose the wood species and grade that best matches your material stamp. Enter the number of plies and actual member size. Built up headers need proper nailing, full bearing, and good contact between plies.
Understanding results
A pass result means the selected header meets the built in assumptions. It does not replace local code design. A fail result means you can reduce span, add plies, choose deeper lumber, increase grade, or reduce load. Deflection may control even when strength looks acceptable. Stiffness often matters for doors, windows, tile, plaster, and masonry finishes.
Good design habits
Headers should sit on adequate jack studs. Bearing length must be checked at each support. Moisture, notches, holes, decay, and poor fasteners reduce performance. Loads from concentrated beams, girders, or trusses may require special engineering. Snow regions, high wind areas, seismic zones, and commercial buildings also need local professional review.
Important limits
The math assumes a simply supported header with even bearing and standard rectangular lumber. It does not model continuous beams, lateral torsional bracing, connection slip, fire damage, hidden defects, or unusual load paths. Treat the output as guidance only today.
Practical use
Use this calculator for early planning and comparison. Try several sizes before buying material. Print or download your results for discussion with a builder, inspector, or engineer. Always verify final header sizing against approved span tables, product data, and local building rules before construction begins.