About the Stair Carpet Calculator
This stair carpet calculator works out how much carpet a staircase needs, either as full-width carpet cut from a broadloom roll or as a continuous stair runner. Each step uses the tread depth plus the riser height plus an allowance for wrapping the nosing, so the calculator measures what actually gets covered rather than the floor plan area of the stairs.
For full-width carpet it lays the steps out across a standard 12 ft roll the way installers do — one piece per step, cut with the pile running down the stairs — and tells you the length of roll to buy and the square yards you will be charged for. For a runner it returns the total running length and area.
Measure one typical step carefully; the nosing allowance (often 1–2 inches) depends on how far the carpet wraps around and under the bullnose. Landings, winders and pie-shaped steps need their own pieces, so measure them separately and add them to the total.
With the default inputs, the length to buy is 6.33 ft. Change any value above to recalculate instantly.
How to use the stair carpet calculator
- 1Count the treads (do not count the top floor or a landing) and decide whether the top riser is carpeted.
- 2Measure one tread depth, one riser height and the nosing wrap.
- 3Choose full-width carpet or a runner and enter its width.
- 4Read the length to buy and the square yards you will be charged.
- 5Add separate pieces for any landing or winder steps.
Formula and method
Carpet follows the profile of each step: across the tread, down the riser and around the nosing, so each step consumes tread + riser + nosing allowance. A staircase has one more riser than it has treads, so when the top riser is carpeted it adds one more strip of riser height plus nosing wrap. A runner is one continuous strip, so its length is the number of steps times the per-step amount plus that top riser.
Full-width carpet is cut as one piece per step with the pile running down the stair. Each piece (including the shorter top-riser strip) is the stair width across the roll and up to the per-step length along it, so the number of pieces that fit side by side is the roll width divided by the stair width (rounded down). The roll length you buy is the number of rows of pieces times the per-step length, and carpet is priced on the full roll width.
- tread, riser
- Tread depth and riser height (in)
- nosing
- Extra carpet to wrap the nosing (in)
- roll, width
- Roll width and stair width (in)
Worked examples
13 straight steps, 36 in wide, full-width carpet
Each step uses 10 + 7.5 + 1.5 = 19 in, and the top riser adds a 9 in strip. Four 36 in pieces fit across a 12 ft roll, so the 14 pieces take 4 rows: 76 in (6.33 ft) of roll, which is 76 sq ft or 8.44 sq yd purchased for 64 sq ft installed.
Same stairs with a 27 in runner
13 steps × 19 in = 247 in, plus 9 in for the top riser and its nosing, is 256 in or about 21.3 ft of runner. At 27 in wide that is 48 sq ft (5.33 sq yd).
14 steps, 11 in treads, 42 in wide
Each step takes 20.25 in. Only three 42 in pieces fit across 144 in, so 14 steps plus the top-riser strip (15 pieces) need 5 rows: 101.25 in (8.44 ft) of 12 ft roll, or 11.25 sq yd.
Frequently asked questions
How much carpet do I need for 13 stairs?+
For typical 10 in treads and 7.5 in risers with a 1.5 in nosing wrap, each step uses 19 in. Cutting 36 in wide pieces four across a 12 ft roll, 13 steps plus the top riser need about 6.3 ft of roll — roughly 8.5 sq yd.
How do you measure stairs for a runner?+
Measure the tread depth, riser height and how far the runner wraps the nosing on one step, add them together and multiply by the number of steps, then add one riser and nosing for the top riser if the runner continues to the upper floor. Measure the width you want the runner to be, leaving an even border of wood on each side.
Which way should the carpet pile run on stairs?+
Installers lay carpet so the pile runs down the stairs, from the back of the tread toward the nosing. This wears better and looks consistent, which is why each step is cut as a separate piece across the roll.
Do I need carpet padding on stairs?+
Yes for most installations. Padding is cut to cover the tread and wrap the nosing but usually not the riser, so it needs a little less material than the carpet itself; use a firm, dense pad for stairs.
How do I handle a landing?+
Measure the landing as a separate rectangle and add its area, or add its depth to the runner length. Offcuts left over from the roll are often large enough to cover a small landing.