Carpet Calculation Method for Stairs
The most reliable way to estimate stair carpet is by calculating the **total lineal length** required to run up the staircase, treating the stairs as one continuous sloped surface. This method is often called the "running foot" method.
The "Tread + Riser" Formula
- **Material per Step:** For each step, you need to cover the **tread** (horizontal part) and the **riser** (vertical part).
- **Bullnose Wrap:** A small allowance (typically 1 inch) is added to account for the carpet wrapping around the rounded front edge (the bullnose) of the step.
- **Total Length:** $\text{Total Lineal Feet} = (\text{Tread} + \text{Riser} + 1 \text{ inch}) \times \text{Number of Steps} / 12$
- **Final Area:** The lineal feet are then multiplied by the stair width (in feet) and the waste factor to find the $\mathbf{Total\ Square\ Yards}$ for purchasing.
Important: Pattern Matching
If you are using patterned carpet, increase your waste allowance to $\mathbf{20\% \text{ or more}}$. Patterned carpets require extra material to ensure the design aligns perfectly from one step to the next, often resulting in significant off-cuts.