HesapHanem

Header Size Calculator

Enter the opening span and load type to get a recommended header size.

How it is calculated

This is a simple lookup on the clear span of the opening, in feet. The rule in the tool: up to 3 ft gives 2x6; over 3 and up to 4 ft gives 2x8; over 4 and up to 5 ft gives 2x10; over 5 and up to 6 ft gives 2x12; anything wider than 6 ft returns "engineered LVL" (laminated veneer lumber), meaning a sized engineered member rather than ordinary dimensional lumber. The span is echoed back to two decimals. The boundaries are inclusive on the upper side, so exactly 3 ft is still 2x6 and 6.01 ft already needs LVL. Whatever you pick in the load selector, the size comes from the span alone: single-floor and roof give the same answer, and the tool does not work with snow load, wall height, species, grade or number of plies. It is a rough guide, not a structural design.

Worked example

An opening 4.5 ft wide under a roof load. The span is above 4 ft and not above 5 ft, so it falls in the third step of the table: 2x10. The tool echoes the span as 4.50 ft and adds a note to verify the result with the local building code. A 4 ft opening would have given 2x8 and a 5.5 ft opening 2x12, while a 6.5 ft opening would have switched to engineered LVL.

Try this example →

Common mistakes

  • Measuring the span to the outside of the trimmers or the rough opening of the finished window instead of the clear span between the supports, which gives the wrong step.
  • Expecting the load selector to change the answer; in this tool the size is the same for single-floor and roof, so a heavier load still needs a separate check.
  • Treating the result as an approved size: the tool echoes a reminder that it is a guideline only, and local code or an engineer decides.
  • Entering the span in metres or inches; the field is feet, so 1.2 m must be typed as about 3.9.
  • Reading "engineered LVL" as a size; it only means the span is beyond what ordinary lumber covers here, and the actual LVL section has to be specified separately.

About this calculator

A header (or lintel) is the horizontal structural member above a door or window opening that carries the load from the wall and roof above down to the studs on either side. The wider the opening's clear span, the bigger — and often the more layered — the header lumber needs to be, and load-bearing walls need larger headers than non-load-bearing partition walls for the same span.

This calculator takes your opening's clear span in feet and estimates a recommended header size from it — 2×6 up to 3 ft, 2×8 up to 4 ft, 2×10 up to 5 ft, 2×12 up to 6 ft, and an engineered LVL beam beyond that. The result depends on span alone; it does not account for whether the wall is load-bearing or what sits above it, so bearing walls in particular need a proper check. It's a starting reference for DIY builders and framers planning a new opening or widening an existing one — always meant to be checked against local building code and, for structural work, an engineer's sign-off.

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  • Editorial team

    Treat the size as a first guess for pricing lumber, not as a framing decision. Residential codes publish span tables that depend on the load, the wall width, the species and the grade, and your local building department can tell you which table applies to your opening. Always confirm before cutting a bearing wall. What is the opening for, a door, a window or a garage, and what sits above it?

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