The terms that govern use of Rafter Length Calculator. The short version: results are estimates for planning — verify before you cut, and your local code governs your build.
Every result on this site is a calculation made from the inputs you provide, offered for planning and layout purposes. Geometry results follow standard framing mathematics; span and size results reproduce published code tables for the conditions stated on those pages. Neither kind of result is a guarantee that a particular rafter is suitable for a particular building.
Verify all measurements and calculations independently before cutting material or building. Lumber dimensions vary, buildings are rarely perfectly square, and inputs entered in error produce results that are wrong in good faith. The cost of checking is a tape measure; the cost of not checking is a roof.
The span and size tools present data from the 2021 International Residential Code for the specific conditions stated on those pages. Building codes are adopted and amended locally: your jurisdiction may use a different edition, different tables, or additional requirements, and its version is the one that governs your project. Nothing on this site substitutes for your local code, a building official's determination, or the advice of a licensed engineer or architect where the work falls outside prescriptive provisions.
The calculators and content are provided free for personal and professional planning use. You may link to any page. Scraping the site in a way that burdens its hosting, misrepresenting its results as engineering certification, or republishing its tables and text as your own is not permitted. Worked examples and chart data may be quoted with attribution and a link.
We work to keep every number right — the editorial policy describes how — but the site is provided as is, without warranty of any kind. Errors reported to us are checked and corrected as described in the editorial policy. The site may change, move or be unavailable without notice, and results produced by earlier versions are governed by the version in force when they were produced.
These terms are governed by the laws of the United States. If any part of these terms is held unenforceable, the remaining parts continue in full effect. These terms are effective from 30 October 2026.