About ToolSite

Roof truss calculations aren't complicated, but they're tedious to do by hand. Builders end up reaching for span tables, doing Pythagorean calculations on job-site scraps of paper, and second-guessing their rafter length before calling a fabricator. We built this tool to eliminate that friction.

This calculator covers six residential truss types (King Post, Queen Post, Fink/W, Howe, Scissor, and Attic) and computes peak height, rafter length, roof angle, linear footage, and estimated material costs in seconds. The math uses standard triangular geometry as defined in IRC Section R802, cross-checked against SBCA span tables for common configurations.

Every calculation follows the same geometric relationships used by professional truss engineers. Peak height is derived from the classic rise-over-run formula: rise = (span ÷ 2) × (pitch ÷ 12). Rafter length uses the Pythagorean theorem on the rafter run (including eave overhang) and the corresponding rise.

Truss counts follow the industry-standard approach: building length divided by spacing, rounded up, plus one end truss. Cost estimates use per-foot rate models calibrated against 2024–2026 SBCA pricing surveys — ranging from $3.50/ft for simple King Post trusses to $6.00/ft for Scissor configurations.

We verify our formula outputs against outputs from commercial truss design software for common residential configurations. The results match within rounding tolerance for spans from 16 to 60 feet.

How We Research and Update Content

Our blog articles and calculator documentation are written by people with hands-on construction experience and reviewed against primary sources: the International Residential Code (IRC), AWC design specifications, and SBCA technical bulletins. We don't publish content we can't verify against industry standards.

Cost data is updated annually based on SBCA pricing surveys and commodity lumber market reports. If you notice a discrepancy between our estimates and your regional market, use the results as a directional guide and get a formal quote from your local truss fabricator. Regional price variation of 20–30% from our mid-range estimates is normal.