What is a Stair Carpet Calculator?
A stair carpet calculator determines the total amount of carpet needed to cover a staircase. Unlike flat flooring, stairs require carpet to cover both the horizontal tread (the part you step on) and the vertical riser (the front face of each step), plus a small allowance for tucking the carpet into the nosing. This means you need more carpet per linear foot than for flat surfaces.
Stair carpet can be installed as a runner (narrower strip centered on the stairs) or wall-to-wall (covering the full width). The calculation method is the same, but the width dimension changes accordingly.
Stair Carpet Formulas
Installation Tips
- Add 2 inches per step for tucking carpet into the nosing at the back of each tread.
- Add extra for landings: Measure landing areas separately and add to the total.
- Waterfall vs. cap-and-band: Waterfall installation drapes carpet over the nosing, while cap-and-band wraps each tread individually. Waterfall uses slightly less material.
- Use carpet padding: Quality padding extends carpet life and improves comfort on stairs.
Worked Example
13 steps with 10" treads, 7.5" risers, and 36" width:
Total length = 1.625 × 13 = 21.1 ft
Area = 21.1 × 3 = 63.3 sq ft (7.0 sq yd)
Frequently Asked Questions
How wide should a stair carpet runner be?
Standard stair runners are 27 inches or 32 inches wide. For 36-inch stairs, a 27-inch runner leaves about 4.5 inches of exposed wood on each side, which is a classic look.
Do I need to carpet the risers?
For wall-to-wall stair carpeting, yes. Both treads and risers are covered. For runners, the risers may or may not be covered depending on the style preference and the stair design.
How much extra carpet should I buy for stairs?
Add 10–15% to your calculated amount for waste, pattern matching, and fitting allowance. If using patterned carpet, you may need even more to align the pattern across steps.