Header Size Calculator

Door and window opening headers from IRC span tables — built-up 2x and LVL equivalent

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Header Framing Gear

A header is only as good as the cut, the nails, and the jacks under each end. These are the tools that turn the table lookup into a wall that will not sag.

DEWALT DCN21PLB 21-Degree Framing Nailer

Nail built-up plies, king-to-jack, and header-to-king per the schedule. After you know the size, this is what assembles it.

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Swanson TA122 Aluminum Rafter Square

Square the header ends, mark jack cuts, and check the king/jack plumb before you commit the nailer.

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Stabila Type 196 48-Inch Box Beam Level

Confirm the header is level and the jacks are not kicked in or out. A 1/4" rack shows up later as a door that binds.

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DEWALT DWE575 7-1/4-Inch Circular Saw

Cut header plies and jack studs to length. Built-up headers need matching lengths or the bearing seat is a lie.

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Franklin Sensors ProSensor M210 Stud Finder

Find existing kings, jacks, and header edges in finished walls before you cut a new opening or sister a sagging member.

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Johnson Level 405 Stair/Square Gauge Set

Clamp to a square for repeatable jack and cripple cuts when several openings share a header height.

View on Amazon →

As an Amazon Associate, TestTalkHQ earns from qualifying purchases.

How to Use This Header Size Calculator

Measure the rough opening (inside jack to inside jack), pick species, jacks per end, wall type, snow (exterior), and building width. Calculate. The result is the smallest built-up header (or LVL equivalent) whose IRC span is at least that opening, with the NJ jack count for that cell.

Pick smallest header where tabulated span ≥ rough-opening width
and NJ ≤ jacks entered when possible

Why tributary width and snow change the answer: Header Size Calculator Guide. Sagging, missing jacks, RO vs board length: troubleshooting. Sawn vs LVL cost: which to use. Scan the full grid: header span table. King/jack stick count is a different tool: stud wall calculator.

Header Size Calculator