Each step needs one tread plus one riser
A runner wraps down each step, so per step you need the tread depth plus the riser height. Multiply by the number of steps, add waste, then turn that length into area with the runner width. Divide square feet by 9 for square yards.
Worked example, 12 steps
| Step | Value |
|---|---|
| Per step (tread 10" + riser 7.5") | 17.5 in |
| 12 steps | 210 in |
| + 10% waste | 231 in = 19.25 ft |
| × 27" runner width | 43.3 sq ft |
| ÷ 9 | 4.8 sq yd |
Match runner width to the stairs: up to 36" wide stairs take a 24" or 27" runner; 36–42" take 27" or 30"; wider take 30" or 36".
Where the waste factor really goes
- Wrapped install. Folding around the nose adds the nosing overhang (about 3/4 to 1 1/4 inch) to every step, so it needs 15 to 20 percent waste versus 10 percent for waterfall.
- Pattern matching. A directional or large-repeat pattern has to line up step to step, which pushes waste to 15 to 25 percent.
- Winders and turns. L-shaped stairs or pie-shaped winder steps can need 20 to 30 percent, since the runner has to be cut and fitted to each odd shape.
Common questions
How much carpet do I need for a 12-step staircase?
For a typical staircase (10 inch tread, 7.5 inch riser, waterfall install), each step needs about 17.5 inches of runner. Twelve steps is 210 inches, plus 10 percent waste is 231 inches, or 19.25 linear feet. At a 27 inch runner width that is roughly 4.8 square yards.
What is the difference between waterfall and wrapped installation?
Waterfall lets the carpet fall straight down the front of each riser, which is faster and wastes less (about 10 percent). Wrapped, or Hollywood, folds the carpet around the rounded stair nose for a tailored look but uses more material (15 to 20 percent) and needs precise cuts.
Why do I add each step's tread and riser together?
One length of runner has to cover both the flat you step on (the tread) and the vertical face beneath it (the riser). Adding them gives the carpet needed per step; multiply by the number of steps for the total run.
