Stair Carpet Calculator

How it works

Carpet on a stair covers each tread, each riser and the stair nose between them, so each step needs the tread depth plus the riser height plus an allowance for wrapping the nose. Landings add their depth. Added up over the staircase, that is the length of carpet the stair takes.

A runner is bought by the length in a fixed width, so the length over the steps and landings, plus a waste allowance, is what to order. Its area follows from the runner width.

For full-width (wall-to-wall) stairs cut from roll goods, each step is cut as its own piece the width of the stairs, with the carpet's length running up the stair as the Carpet and Rug Institute's installation standard (CRI 105, 2019, §15.4) recommends. Pieces are laid side by side across the roll, so a 12 ft roll yields four 36 in pieces per row, and the roll length needed is the number of rows times the length of one step. Roll goods are bought by the full roll width, so the area is the linear feet times the roll width.

Formula

per step     = tread + riser + nosing wrap
run length   = steps × per step + landings × landing depth
runner:      linear ft = run length × (1 + waste % ÷ 100)
             area = linear ft × runner width
full width:  pieces across = roll width ÷ stair width, rounded down
             linear ft = (⌈steps ÷ pieces across⌉ × per step
                          + ⌈landings ÷ pieces across⌉ × landing depth) × (1 + waste % ÷ 100)
             area = linear ft × roll width
square yards = square feet ÷ 9

Example

12 steps with 10 in treads, 7.5 in risers and 2 in of nosing wrap take 19.5 in of carpet per step, 234 in or 19.5 ft in all. A 30 in runner with 10% waste is 21.45 linear ft, which is 53.6 sq ft or 5.96 sq yd.

Full width instead: 14 steps of the same size, 36 in wide, cut from a 12 ft roll. Four pieces fit across the roll, so 14 pieces need 4 rows of 19.5 in, which is 6.5 ft, or 7.15 linear ft with 10% waste. At the full 12 ft roll width that is 85.8 sq ft, or 9.53 sq yd.

Assumptions and limitations

• The nosing wrap default of 2 in is a typical allowance, not a standard; the real figure depends on the shape of the stair nose. A waterfall fit, where the carpet drops straight from the nose to the next tread, needs little or none; a cap-and-band or upholstered fit that follows the underside of the nose needs more.
• All steps are the same size. Winders, bullnose steps and open-sided stairs need more material than this model gives.
• Landings are taken to be the same width as the stairs and are cut as separate pieces.
• Runner widths and the 10% waste allowance are typical values. Pattern matching on a patterned runner can need more.
• The result is an estimate. It is not a substitute for a measure by the installer, the carpet manufacturer's instructions or the stair requirements of your local building code.

Frequently asked questions