Stair runner calculator

Total run (treads × tread depth) is a horizontal, floor-plan measurement. A runner, though, follows the actual surface of the stair: across each tread, down over the nosing, and down the face of each riser before starting the next tread. That path is close to the stringer length but slightly longer because of the extra nosing wrap.

For a flight with 13 treads at 10.5 in and 13 risers at 7.5 in, the per-step surface length is roughly tread + riser + a small nosing wrap allowance (about 1 in), or about 19 in per step, versus a raw tread depth of only 10.5 in.

Runner length ≈ treads × (tread depth + riser height + nosing wrap) + landing/top-bottom allowance, then add a waste percentage. Using 13 treads, 10.5 in tread, 7.5 in riser, and 1 in nosing wrap: 13 × (10.5 + 7.5 + 1) = 13 × 19 = 247 in.

Add a top and bottom finishing allowance (extra length to tuck under a pad at the top landing or to fold under at the bottom) of a few inches, then apply waste, commonly cited around 10 percent to cover pattern matching and installer trim losses: 247 × 1.10 ≈ 271.7 in, about 22.6 ft, or roughly 7.5 yd.

1. Count the number of treads in the flight, including any winder or landing treads if the runner continues through them.
2. Measure tread depth (front edge to front edge, or nosing to nosing) and riser height on at least two steps to confirm consistency.
3. Measure stair width to confirm the runner width you want (commonly 27 in or 32 in, chosen to leave an even reveal of exposed wood or floor on each side).
4. Add the top allowance (extra length at the top landing for tucking or binding) and bottom allowance (extra for a waterfall fold or bound end).
5. Apply a waste percentage, higher for patterned runners that need to match repeat points step to step, lower for solid colors.

Stock stair runner widths are commonly cited around 27 in and 32 in, though narrower and wider options exist. The width you choose interacts with your stair width: a common look leaves a roughly equal reveal of exposed tread or floor on each side, so measure stair width first and subtract the runner width to check the reveal before ordering.

A Hollywood install wraps the runner over the nosing and tucks it tight into the angle where the tread meets the riser below, following the stair's actual profile closely. This uses close to the calculated per-step length with a small wrap allowance and gives a tailored, close-fitting look.

A waterfall install lets the runner fall straight down the face of each riser without tucking into the nosing angle, so it uses slightly less length per step but leaves a small triangular gap visible under each nosing. Waterfall is generally faster to install; Hollywood looks more finished but uses marginally more material and installer time.

If the runner has a directional or repeating pattern, order extra length so the pattern lines up consistently from step to step, since the installer may need to cut around a repeat rather than starting a new length at an arbitrary point. Pattern goods commonly need a higher waste allowance than the roughly 10 percent used for solids, sometimes 15–20 percent depending on the repeat size.

• Ordering based on total run alone instead of the wrapped surface length, coming up noticeably short.
• Forgetting the top and bottom finishing allowance needed for tucking, binding, or a waterfall fold.
• Skipping a waste allowance on patterned goods, which can leave mismatched repeats at the bottom of the flight.
• Not counting winder or landing treads that the runner still needs to cover.