ToolwickStair Carpet Calculator
This free stair carpet calculator tells you how many square yards and linear feet of carpet you need to cover a staircase, plus the pad and tack strip to buy with it. Enter your risers, rise, run and width, and waste is included automatically.
How to Use This Stair Carpet Calculator
Count the risers (the vertical faces) on your staircase, then measure one rise, one run (tread depth from nosing to nosing) and the stair width. Pick waterfall or cap-and-band, wall-to-wall or runner, and set the waste slider. The calculator returns carpet in square yards and linear feet, the amount billed from a standard roll, pad, tack strip and an optional cost estimate. Everything is rounded up so you do not come up short.
Why This Matters
Stair carpet is one of the easiest jobs to under-order. A typical 13-riser staircase is only about 6.4 square yards of actual surface, yet the carpet you pay for is often four times that, because broadloom is sold off a 12-foot-wide roll and a 36-inch staircase only uses a quarter of that width. Knowing the true linear footage lets you ask a retailer about remnants, bound runner stock or a cut from the edge of a roll before you commit.
It also matters for pattern and nap. Stairs are cut as one long strip so the pile runs the same way down every step, and you cannot patch a short piece in later without it showing. If you order 20 feet and need 21, you may be buying a whole new dye lot. Homeowners recarpeting before a sale, landlords turning over a rental, and contractors quoting a remodel all need a number they can trust: enough carpet, enough pad, enough tack strip, and a realistic budget. A few minutes with this tool, plus a tape measure, usually saves a second trip to the store and a few hundred dollars in mistakes.
How It's Calculated
Carpet follows the profile of the stairs: up the riser, across the tread, over the nosing. The calculator adds those pieces together, applies your waste percentage, and rounds up to the next whole inch of length.
Length with waste = Length × (1 + waste %), rounded up
Area (sq yd) = length (ft) × width (ft) ÷ 9
Treads equal risers minus one when the top riser meets the upper floor, because that last "tread" is the floor itself. Cap-and-band adds 2 inches per riser for the extra tuck on each separate piece. For wall-to-wall carpet the "billed" area is length × roll width ÷ 9, since the unused width of the roll is normally still charged. Tack strip assumes two width-long strips per riser plus 10%, and pad equals your carpet area.
This is a planning rule of thumb, not an engineering, permit or inspection result. Riser and tread values are only compared with the common IRC R311.7.5 limits (7¾ in maximum rise, 10 in minimum run) as a heads-up. Local codes vary, so check yours before changing a staircase.
Worked Example
A straight staircase has 13 risers, a 7.5 in rise, a 10 in run, is 36 in wide, and meets the upper floor. We use a waterfall install, 1 in allowance, 10% waste and a 12 ft roll.
- Risers: 13 × (7.5 + 1) = 110.5 in
- Treads: 12 × 10 = 120 in, for a total of 230.5 in
- With 10% waste: 230.5 × 1.10 = 253.55, rounded up to 254 in, or 21.2 ft
- Area: 21.17 ft × 3 ft = 63.5 sq ft, or 7.1 sq yd of carpet and 7.1 sq yd of pad
- Billed from a 12 ft roll: 21.17 × 12 ÷ 9 = 28.3 sq yd, which is $707.50 at $25 per sq yd
- Tack strip: 13 × 2 × 3 ft = 78 ft, plus 10% = 86 ft, or 22 four-foot strips
Switching to a 27 in runner drops the carpet to about 5.3 sq yd, which is why runners are popular on a budget.
Tips & Common Mistakes
- Measure several steps. Older houses have uneven risers. Use the largest rise and run you find, or enter the average and raise the waste slider.
- Count risers, not treads. The number of risers is the number of steps you climb. The top tread is usually the floor.
- Include the carpet and pad thickness mentally. Together they can add about ½ in at each nosing, and uneven thickness is a trip hazard. Use a firm, low-profile pad rated for stairs.
- Mind the pile direction. Pile should lean down the stairs. Tell the installer so the strip is cut and stretched the right way.
- Ask about remnants. Because you pay for roll width, a remnant or bound runner can cost far less than a full cut. Confirm the dye lot if you add landings later.
Frequently Asked Questions
How much carpet do I need for 13 stairs?
With a typical 7.5 in rise, 10 in run and 36 in width, plan on about 21 linear feet or roughly 7 square yards after 10% waste. If you buy broadloom off a 12 ft roll, you may be billed for about 28 square yards. Use the calculator for your exact dimensions.
How do you measure stairs for carpet?
Measure the rise from tread to tread, the run from nosing to nosing, and the width wall to wall (or the runner width you want). Count the risers. Add the landings you plan to cover, then include 10–15% for waste.
What is the difference between waterfall and cap-and-band?
Waterfall uses one continuous piece that flows over each nosing and down the next riser. Cap-and-band uses a separate piece for each tread and riser, which is more labor and about 2 in more carpet per step, but it lets you use remnants and choose a contrasting band.
How much waste should I allow for stair carpet?
Ten percent is a sensible minimum for straight stairs with plain carpet. Use 15% or more for patterned carpet, winders, curved stairs or if you are installing it yourself for the first time.
Do I need pad under stair carpet?
Yes. Pad protects the carpet from wear on the nosing and gives a firmer, safer feel. Use a dense, thin pad made for stairs, typically ⅜ in or less, and cut it the same width as the carpet.
Is a runner cheaper than wall-to-wall stair carpet?
Usually, yes. A 27 in runner uses less than a full-width carpet and is often sold by the linear foot. You do give up the full-coverage look, and you will need to bind or finish the edges and add stair rods or clips if desired.
Results are estimates for planning and ordering only. They are not engineering, permit or code-inspection approval, and local building codes vary.