Lintel Header Size Calculator

A header interrupts the vertical load path through a stud wall and carries everything above the opening sideways to the jack studs at each end. It is modeled as a simply supported beam whose span is the clear opening plus the bearing at each end, typically 1.5 inches per jack stud, which is why this tool adds about 0.25 feet to the stated opening width. The uniform load w combines the tributary roof or floor load, taken as half the joist or rafter span on each side, plus the self weight of the wall above at roughly 7 to 10 psf of wall area. From w the moment follows as wL-squared over 8, the required section modulus is that moment divided by the allowable bending stress, and the required moment of inertia comes from holding deflection to L/360 so that drywall and trim above the opening do not crack. Common built-up headers give a useful sense of scale: a doubled 2x8 provides a section modulus of 26.28 cubic inches, a doubled 2x10 provides 42.78, and a tripled 2x12 provides 94.92. Sawn No. 2 lumber is usually taken at 1,000 to 1,200 psi in bending, while laminated veneer lumber reaches roughly 2,600 psi, which is why a single LVL ply often replaces a doubled sawn header. The calculation here assumes uniform loading only. It does not check compression perpendicular to grain at the jack studs, where allowable stresses are only about 425 to 625 psi, and it does not handle concentrated loads from girders or posts landing near the opening.

The post and lintel is among the oldest structural arrangements humans built. Stone lintels span the uprights at Stonehenge, raised around 2500 BC, and trabeated stone construction defined Egyptian temple halls and Greek temple porticoes. The governing limitation was always the same: stone is far weaker in tension than compression, so lintel spans stayed short and openings stayed narrow. That constraint is a large part of why Roman builders adopted the arch so enthusiastically, since an arch carries the same opening in compression alone. Masonry practice later turned to iron and then steel angle lintels, which is why the term lintel still attaches to masonry work while header attaches to framed walls. Wood headers as a distinct sized component belong to the light-frame era that began with balloon framing in the 1830s and became platform framing in the twentieth century. For most of that period builders worked from convention rather than calculation. Prescriptive header tables entered American residential codes through the CABO One and Two Family Dwelling Code, and when the International Code Council consolidated the regional model codes into the first International Residential Code in 2000, those tables became Table R602.7. Engineered options expanded the range considerably: laminated veneer lumber was commercialized in the early 1970s and parallel strand lumber followed in the 1980s, letting a single slender ply span openings that would otherwise demand a deep multi-ply assembly.