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King Post Truss Member Length Calculator

Calculate top chord and king post member lengths for a simple king post roof truss.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax
26.25 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

King post length

6.56 ft

High confidence
Top chord length (each side)
14.67 ft

Running these inputs gives 2 m as the king post length. Top chord length (each side) carries the most weight in this calculation, at 4.47 m. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • King post truss geometry: top chord length = half-span × √(1+(pitch/12)²); king post (vertical) length equals the ridge rise = half-span × (pitch/12)

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does the king post length equal the ridge rise?
In a king post truss, the vertical king post runs from the centerline of the bottom chord straight up to the ridge (peak) of the two top chords — since it's plumb and centered, its length is exactly the vertical rise at midspan, half-span × (pitch/12).
Why is the top chord longer than the king post for the same truss?
The top chord runs along the sloped roof line from the bearing to the ridge, so its length includes both the rise and the horizontal run (half-span) combined via the slope factor √(1+(pitch/12)²) — it's always longer than the vertical-only king post for any positive pitch.
Does this include the web (diagonal strut) members of the truss?
No — a basic king post truss's diagonal struts run from the king post to the mid-point of each top chord; their lengths depend on where along the top chord they connect and aren't included in this top-chord and king-post-only calculation.