How to Carpet Stairs

There are two install styles and they consume slightly different amounts of carpet. In a waterfall install the carpet runs straight off the front of each nosing and drops vertically to the next tread — fast, and it uses a little less material. In a cap-and-band (also called "upholstered") install the carpet is wrapped tightly around and under each nosing for a tailored look, which adds a wrap allowance per step.

The carpet style is an input, not an afterthought: pick it before you measure, because cap-and-band needs that extra wrap on every tread. Our stair carpet calculator lets you choose waterfall or cap and applies the right nosing-wrap allowance automatically.

1. Measure the tread run (front to back of the walking surface), e.g. 11″.
2. Measure the riser height (the vertical face), e.g. 7³⁄₁₆″.
3. Add a nosing wrap allowance of about 1½″ for waterfall, more for cap-and-band.

Add the tread, riser, and wrap for one step, then multiply by the number of treads to get the total runner length. For the canonical 15-tread flight, 11″ tread + 7³⁄₁₆″ riser + 1½″ wrap is about 19⁵⁄₈″ per step, so the runner runs roughly 24′-7″ long. That is a striking number — nearly twenty-five feet of carpet for a staircase whose floor plan footprint is barely thirteen feet — and it is the single biggest reason people under-order.

Carpet is sold by the square yard, so multiply the runner length by the runner width and divide by nine (square feet per square yard). A 27″ runner over that flight is about 4.7 square yards before waste. Buy carpet in a single continuous length wherever you can — a seam on a stair is a wear point and a trip hazard, and on a curved or pie-shaped tread a seam is nearly impossible to hide. The stair carpet calculator returns both the runner length and the square yardage so you can order one piece.

Add a waste margin — our calculator includes a 5% allowance — for trimming, pattern matching, and the occasional miscut. That margin is small but it matters: stairs are the one place where running a foot short means an ugly seam in a high-wear, high-visibility spot rather than a hidden joint under a sofa.

If the carpet has a directional pile or a pattern, all the pile must run the same way down the stairs so it brushes "with" the foot traffic and wears evenly, and so the color reads consistently from top to bottom. Keeping the pile direction and the pattern aligned tread to tread can force extra length, especially on a patterned runner where each step has to start at the same point in the repeat. Factor that in before ordering, and when in doubt buy the next half-yard up.

A straight flight is the easy case. If your stairs turn — an L-shaped or U-shaped run with a landing, or winders that fan around a corner — measure each straight section as its own runner and treat the landing as a separate flat piece. Winder treads are pie-shaped and wider at the outside, so they consume more carpet than a rectangular tread and almost always need their own cut rather than a continuous runner.

Add the runner lengths of each straight flight, plus the landing area, plus any winder pieces, to get the total order. Because seams are unavoidable where a runner meets a landing, plan those joints to fall at the back of a tread or the inside of a turn where foot traffic and sightlines are lightest. The stair carpet calculator sizes each straight run; add the landing and winder areas to its figure for the full job.

Decide early whether you are laying a narrow runner that leaves the tread edges exposed or carpeting the full tread width wall to wall. A runner — typically 27″ or 33″ wide — shows a border of finished wood on each side and uses less carpet, but it has to be centered perfectly or it reads crooked all the way up. Full-width carpet covers the whole tread, hides the stringer line, and is more forgiving to install, but it uses more material because the width is the full stair width rather than the runner width.

Either way, the runner length math is identical — it is only the width term in the yardage that changes. Set the width in the stair carpet calculator to match your choice so the square-yard figure is right for the job you are actually doing.

You will need carpet, a matching pad or underlay cut to the tread depth, tackless strips for the crotch of each step, a knee kicker or stair tool, a sharp knife, and a stair tucker. Set tackless strips in the angle where each tread meets its riser, points facing into the crotch, lay the pad over each tread and wrap it just over the nosing, then work the runner from the bottom up, kicking it tight into each crotch and tucking the edges so there are no loose spots to catch a heel.

Take your time on the first tread — it sets the alignment for the entire run, and a runner that starts a half-inch off center never recovers. If you also need the surface area for paint, stain, or hard flooring on the same stairs, the stairs square footage calculator gives the tread, riser, and stringer-face area, and the stairs cost calculator will price the materials and labor for the whole job.