Stair Carpet Calculator
Find how much carpet to buy for a straight staircase, or how long a stair runner to order. Enter the number of steps and the tread, riser, and width of one step, then choose the roll width to see the strips to cut from the roll, the joins, and the length to order. Add prices for carpet, pad, and installation to estimate the total.
- Choose US or Metric. You can still change the unit of any single field.
- Count the Steps: every step up, including the last one onto the floor above. This is the number of risers, the same number the Stair Calculator shows as Risers.
- Measure one step. The Tread depth runs from the riser at the back to the front edge of the nose, the Riser height from the top of one tread to the top of the next, and the Stair width across the tread, wall to wall or to the open edge.
- Check the Extra per step, which starts at 2 in or 5 cm for wrapping the nose and trimming.
- Choose the Roll width. For another width, choose Custom width. For a runner cut to length, choose Runner and enter the runner width as the Stair width.
- Optionally, enter prices for carpet, pad, and installation. Carpet can be priced per ft² or m², or per ft or m for a runner, and installation per step.
Length fields accept whole numbers, decimals, fractions, and mixed
numbers, such as 10, 7.5, 3/4, or
36 1/8.
How much carpet you need for stairs
Each step takes a piece of carpet that covers the tread and the riser below it, plus a little extra to wrap the nose and trim. The UK retailer Online Carpets and the flooring company The Flooring Group both work out stair carpet this way: tread plus riser plus 5 cm, times the number of stairs.
Each step = tread depth + riser height + extra per step
Length up the stairs = steps × each step
Carpet comes off a roll of a fixed width, so the calculator cuts strips as wide as the stairs from the roll and lines the steps up along each strip, as Online Carpets lays out a 4 m roll for its stairs:
Strips from the roll = roll width ÷ stair width, rounded down
Steps per strip = steps ÷ strips from the roll, rounded up
Carpet to buy = roll width × (steps per strip × each step)
Every strip is cut to the same length, and each step stays in one strip, so the strips end at the back of a tread. These are the Joins. A wider roll gives more strips, which can shorten the length you buy. With Runner, the roll is as wide as the stairs, so there's one strip, and the carpet to buy is the length up the stairs.
The strips run up and down the stairs. The Carpet and Rug Institute's CRI 105 installation standard recommends running the length of the roll up the stairs, and notes that most makers want the pile running down them. Turning the strips the other way could use less carpet, but the pile would run across the steps, so the calculator doesn't offer it.
The calculator doesn't add a waste percentage. The part of the strips you don't use is shown as Offcuts, the carpet to buy minus the stair area. The extra per step and the whole steps in each strip already leave room for trimming.
The last step is counted like the others, with a tread. If the carpet stops under the nose at the top, as the US retailer Rugs Done Right describes for runners, the last piece only needs the riser, so you may have one tread to spare.
Measuring stairs for carpet
- Steps. Count the risers, including the last one onto the floor above. If you're building the stairs, use the Risers from the Stair Calculator.
- Tread depth. The Flooring Group measures the tread from the edge of the stair to the riser. Measure to the front of the nose, because the carpet covers it. This is more than the tread depth in the Stair Calculator or the US building code, which is measured between the fronts of two noses. The code allows a nose of 3/4 in to 1 1/4 in.
- Riser height. Measure from the top of one tread to the top of the next.
- Several steps. Steps aren't always the same size, so The Flooring Group suggests measuring several. Enter the largest.
- Stair width. Measure across the tread, wall to wall or to the open edge. The calculator doesn't add anything to the width, so a 36 in stair fits 4 strips on a 12 ft roll. Online Carpets adds 5 cm on each side for trimming. To leave room to trim at the walls, add it to the stair width, but a wider strip can mean fewer strips from the roll.
- Open sides. If a side of the stairs is open and the carpet is turned under or wrapped around the side, add that to the stair width too. For a turned edge, CRI 105 keeps the tack strip and pad about 1 1/2 in narrower than the carpet.
Extra per step
| Units | Extra per step |
|---|---|
| US | 2 in, the larger of the inch or two for the nose in Bob Vila |
| Metric | 5 cm, from Online Carpets and The Flooring Group |
The extra covers the nose and trimming. A waterfall installation drops the carpet straight from the nose to the next tread. A Hollywood (cap-and-band) installation follows the nose and fastens under it, which Bob Vila puts at about an inch more per step. Both fit in 2 in or 5 cm. Increase it for a deep nose, or when the tread and riser are cut as separate pieces.
Landings, runners, and other stairs
Landings and hallways
Measure a landing or the hallway at the top like a room, in the Carpet Calculator, with the same roll width, and add that carpet to the stairs. Online Carpets includes the riser in a landing, so add one riser height to the landing's depth, and leave the step up to that landing out of the Steps here. Otherwise the riser is counted twice. This applies to a landing partway up and to the floor at the top when it gets the same carpet.
Stair runners
A runner leaves the sides of the treads bare. Rugs Done Right sells runners cut from a roll by the linear foot, in widths from 20 in to 48 in, with 27 in the most common. Choose Runner, enter the runner width as the Stair width, and use Length up the stairs as the length to order. To price it, choose per ft or per m for the carpet price. For a ready-made runner sold in set lengths, choose one at least as long as the length up the stairs. For stair treads, the mats sold one per step, buy one for each step.
Winders, bullnose steps, and patterned carpet
The calculator lays out straight steps that are all the same size. Online Carpets and the UK retailer Flooring Hut measure winders, the wedge-shaped steps where a stair turns, one at a time, and Bob Vila notes that a bullnose step, a wider bottom step with a rounded end, needs extra carpet. Enter only the straight steps, and check the rest with your retailer or installer. Flooring Hut also warns that roll width and pattern matching change how much carpet stairs need. CRI 105 notes that patterned carpet needs extra material, so check a patterned or striped carpet with your retailer or installer as well.
Examples
13 carpeted steps
With 10 in treads, 8 in risers, and 2 in extra, each step takes 20 in, and 13 steps take 21 ft 8 in. A 12 ft roll gives 4 strips 36 in wide, so up to 4 steps go in each strip of 80 in. Buy 12 ft × 6 ft 8 in, 80 ft² or about 8.89 yd², with 3 joins. The stairs cover 65 ft², so 15 ft² is offcuts. With 12 steps, 3 go in each strip, and 12 ft × 5 ft, 60 ft², leaves no offcuts. From a 15 ft roll, the 13 steps fit in 5 strips of 3, 15 ft × 5 ft, 75 ft².
If you add trim to the width and enter 36 1/8 in, only 3 strips fit, and the carpet grows to 12 ft × 8 ft 4 in, 100 ft².
The cost with pad and installation
For the same 13 steps, carpet at $2.50 per ft², pad at $0.60 per ft², and installation at $15.00 per step cost 80 × $2.50 = $200 for the carpet, 65 × $0.60 = $39 for the pad, and 13 × $15 = $195 for installation. The total is $434. The pad uses the stair area, not the carpet you buy.
A stair runner
For a 27 in runner on the same 13 steps, order 21 ft 8 in, 27 in × 21 ft 8 in or 48.75 ft². At $30.00 per ft, that's 21.67 ft × $30 = $650.
Metric dimensions
For 13 steps with 25 cm treads, 18 cm risers, and 5 cm extra, each step takes 48 cm, and the stairs take 6.24 m. A 4 m roll gives 4 strips 90 cm wide, so buy 4 m × 1.92 m, 7.68 m², for a stair area of 5.62 m². From a 3.66 m roll, it's 3.66 m × 1.92 m, about 7.03 m².
FAQ
For typical steps with 10 in treads, 8 in risers, and a 36 in width, about 12 ft × 6 ft 8 in, or 80 ft², from a 12 ft roll. Each step takes about 20 in, so the steps cover 21 ft 8 in, cut into 4 strips. Enter your own measurements for an exact figure.
Count the risers, including the last one onto the floor above. On one step, measure the tread from the riser to the front of the nose, the riser from the top of one tread to the top of the next, and the width across the tread. Measure several steps and use the largest.
The number of steps times the tread, riser, and a little extra for each step. For 13 steps of 10 in treads and 8 in risers with 2 in extra, that's 21 ft 8 in. Choose Runner and enter the runner width to see it.
No. Each step already includes extra for the nose and trimming, and the strips are cut in whole steps. The unused part of the roll is shown as Offcuts.
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