The Golden Rules of Stair Building
Building stairs is one of the most mathematically demanding tasks in construction. The primary goal is to ensure consistency and safety, which is governed by building codes (like the International Residential Code or IRC).
Key Building Rules
- **Maximum Riser Height:** The height of the vertical part (riser) should not exceed **$7.75$ inches** (IRC) or $8.25$ inches (used in this calculator for common use). All risers must be the same height.
- **Minimum Tread Depth:** The depth of the horizontal part (tread) should be at least **$10$ inches** (IRC). All treads must be the same depth.
- **The Comfort Rule (The "17-18 Inch Rule"):** For optimal human comfort, the sum of the $\mathbf{Riser\ Height}$ and $\mathbf{Tread\ Depth}$ should be between **$17$ and $18$ inches**. This ensures a natural walking gait.
The First Step is Different
The calculation is always for the total rise. However, when cutting the stringer, the **first riser cut** at the bottom is often shortened by the thickness of the tread material to account for the finished floor height.