Stair runner length = steps × (tread + nosing + riser), plus any landings and a little spare. Fourteen steps of 10 in tread, 1 in nosing and 7.7 in riser come to 18.7 in a step, 21 ft 9¾ in on the stairs and 22 ft 7 in with half a step spare, so buy 23 ft, which is 7⅔ yards. The same sum works for stair carpet, and the calculator gives the metric answer in meters.
How stair runner length is calculated
A runner is laid over the tread, wrapped over the nosing and taken straight down the riser to the next tread. That path is the tread board depth (your tread plus the nosing) plus one riser height, about 18 to 19 in on a standard stair. Multiply by the number of steps, add landings, and round up. Installers usually order more than the bare sum: the DirectCarpet measuring guide uses (steps + ½) × 19 in and rounds up to the next foot, which is why the calculator adds half a step of spare length by default. Switch it off if your supplier wants the exact figure.
Length = steps × (tread + nosing + riser) + landings × landing depth + ½ step. Runner width = stair width − 2 × bare stair each side. Rods = one per step, two brackets each.
The default stair works out as 14 × 18.7 = 261.8 in, plus 9.35 in of spare, is 271.15 in, or 22 ft 7 in. Round up to 23 ft; in yards that is 7.67. With one 36 in landing carried across, the total is 307 in and you order 26 ft. In metric, 14 steps with 255 mm treads, 25 mm nosings and 195 mm risers use 6.89 m, so buy 6.9 m.
Stair runner width
Leave 3 to 4 in of bare stair on each side, which makes a runner 6 to 8 in narrower than the stair, according to the same guide. For a 36 in stair that is 28 to 30 in, and the most popular width is 28 in. Show less wood (2 to 3 in) to hide worn treads, or more (4 to 6 in) to show off good hardwood. The calculator takes the bare stair as an input and prints the runner width; set it to your own reveal. Check the width you buy with the runner's maker, since standard widths are not always the ones you calculate.
Stair carpet: covering the whole stair
Choose "Full width carpet" to cover the steps from wall to wall. The calculator multiplies the same length by the stair width, adds a waste allowance (10% by default, for cuts and pattern matching) and gives square yards or square meters. For the default 36 in stair that is 67.8 sq ft, or 8.3 sq yd with waste. Carpet on stairs is normally cut from a roll and fitted step by step, so ask your fitter how much of the roll their layout uses. For the carpet in the rooms around the stair, use the carpet calculator.
Stair rods
Rods hold the runner in the crease of every step. One rod and two brackets per step is the usual count, so 14 steps take 14 rods and 28 brackets. Rod length has to cover the runner width plus the finials; the runner width the calculator prints is the number to start from.
Landings and turns
A straight landing adds its depth to the length. Measure landings separately and add them, as the guide says. Winders and curved stairs are a job for a template: the tread depth changes across the step, so the sum above does not apply. Check the steps themselves with the stair calculator, and if you are building the stair, the stair tread calculator counts the boards and the stair landing calculator sizes the landing. Space the rail with the baluster spacing calculator. All the stair tools are on the decks and stairs hub.