Understanding your result
For a full-width carpet the headline is the carpet in square yards; for a runner it is the runner length. The stats give the carpet per step, the area and the pad; the table shows the steps, the length for the flight, the width, the area of the flight and the landings, the total, and the pad and rods.
Carpet per step is the tread, the riser and 1.5 in for the wrap over and under the nosing. With a pattern repeat, the figure is rounded up to the next whole repeat, because each step must start at the same point of the pattern or the design zigzags down the stairs. The flight is that figure times the number of steps.
Width for a full-width carpet is the stair width plus 3 in to tuck at the sides; for a runner it is the runner’s own width. Landings are added as an area with 10% for the cuts, and for a runner they become extra length at the runner’s width. The pad covers each tread inside the tuck, not the risers. For hard flooring on stairs, the stair flooring calculator counts treads, risers and nosings; for the carpet in the rooms either side, the carpet calculator; for the pad grade, the carpet padding calculator.
How we calculate this
The 1.5 in nosing allowance follows the usual cap-and-band or waterfall installation over a rounded nosing. Pattern rounding is the worst case; an installer may match more economically. The pile direction and the pad guidance come from the Carpet and Rug Institute’s residential installation standard, CRI 105. The guide to carpeting stairs compares runner and full-width installations, waterfall and Hollywood styles, and the carpet padding guide explains why stairs need a firmer pad than rooms.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Tread and riser | 10 in and 7.5 in | Typical US stairs; IRC R311.7 allows a 7 3/4 in maximum riser and a 10 in minimum tread |
| Nosing wrap | 1.5 in per step | Installer practice for a rounded nosing |
| Side tuck | 1.5 in each side (full width) | Installer practice |
| Runner width | 27 in (69 cm) | Common runner width for a 36 in stair |
| Pile direction | down the stairs | CRI 105 |
| Pad | 8 lb or firmer, 7/16 in maximum | Carpet manufacturer and CRI guidance for stairs |
| Landings | +10% | Cutting allowance |
Assumptions last reviewed October 8, 2026.
The calculator assumes straight steps of equal size. Winders, pie-shaped steps and the bullnose bottom step need more; measure each odd step as an area and add it to the landings. On an open-sided stair the carpet also wraps the exposed end of each tread, which adds a few inches per step. And it does not count the tack strip exactly; the shopping list estimates two pieces per step.
Two worked examples
A 14-step flight, full-width carpet
10 in treads, 7.5 in risers, 36 in wide, $45 per square yard.
- Per step: 10 + 7.5 + 1.5 = 19 in; flight 14 × 19 = 266 in = 22.2 ft
- Width: 36 + 3 = 39 in
- Carpet: 22.2 × 39 ÷ 12 = 72 sq ft = 8.0 sq yd, $360
- Pad: about 32 sq ft
Eight square yards for one flight. Because the pile must run down the stairs, the dealer cuts a strip 39 in wide along the roll; the rest of that roll width is offcut unless it is used for a hall or a closet.
A patterned runner on 13 steps with a landing
11 in treads, 7 in risers, 27 in runner, a 9 in pattern repeat, a 12 sq ft landing, stair rods.
- Per step: 11 + 7 + 1.5 = 19.5 in, rounded up to the next whole repeat = 27 in
- Flight: 13 × 27 = 351 in = 29.3 ft
- Landing: 12 × 1.1 = 13.2 sq ft ÷ 2.25 ft = 5.9 ft
- Runner: 35.1 ft; 13 stair rods
The pattern adds 7.5 in to every step, 8 ft over the flight. A runner with a shorter repeat, or one that happens to divide evenly into 19.5 in, would save most of it.
Where to find your inputs
Steps. Count the risers from bottom to top; the landing at the top is the upstairs floor.
Tread and riser. Measure one typical step: tread from the back of the step to the front of the nosing, riser from tread to tread.
Width. Wall to wall, or wall to the edge of an open side.
Pattern repeat. From the runner’s product page.
Common mistakes
- Pile running up the stairs. It catches and wears on the nosings. Cut along the roll so the pile runs down.
- Soft, thick pad. The carpet rolls over the nosing and wears through. Use dense pad, 7/16 in at most.
- Ignoring the pattern. A runner pattern must line up on every step.
- Measuring one step and assuming all are equal. Older stairs vary. Check the top and bottom steps.
- Forgetting the landings. Add them as an area.
- Open sides not counted. Wrapping the side of each tread adds carpet.
Questions people ask
- How much carpet do I need for 13 stairs?
- Each standard step takes about 19 inches of carpet, a 10 inch tread, a 7.5 inch riser and 1.5 inches around the nosing, so 13 steps take about 20 ft 7 in of length. At 39 inches wide (a 36 inch stair plus tucks) that is about 67 sq ft or 7.4 sq yd.
- How long a runner do I need for my stairs?
- Multiply the carpet per step, usually 18 to 20 inches, by the number of steps, and add any landings. Thirteen standard steps need about 21 ft of runner; a patterned runner needs more because each step must start at the same point of the pattern.
- How wide should a stair runner be?
- Usually 27 inches on a 36 inch stair, leaving 4 to 5 inches of wood showing each side. Wider stairs take wider runners; the gap at each side should look even and is often 3 to 5 inches.
- Which way should the pile run on stairs?
- Down the stairs, from the top tread toward the bottom. The Carpet and Rug Institute's installation standard calls for it because pile running up the stair catches and wears on the nosings. That is why stair carpet is cut along the roll.
- What pad goes on stairs?
- A dense pad, 8 lb rebond or firmer, no thicker than 7/16 inch, cut to each tread and stopping short of the riser and the sides. A soft or thick pad lets the carpet roll over the nosing and wear through quickly.
- How many steps are in a flight of stairs?
- A typical one-storey flight in a US house has 13 to 14 risers for a floor-to-floor height of about 9 to 10 ft. The residential code limits risers to 7 3/4 inches and treads to at least 10 inches.