Enter stair details and allowances to get carpet length, width, area & total cost
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Staircases are the one part of a carpet job that cannot be estimated from a simple room measurement. Each step consumes both its horizontal tread and its vertical riser, every step adds a nosing allowance if you wrap the front edge, and a landing at the top or bottom adds a whole extra strip that runs perpendicular to the flight. Add pattern matching waste, side-tuck allowance and the roll width your supplier actually stocks, and a rule-of-thumb figure quickly loses touch with reality. This stair carpet calculator builds the estimate the way an installer does: step-by-step along the flight, then widened and lengthened for the practical allowances that matter. It suits carpet fitters pricing a job, homeowners replacing a staircase, and anyone comparing per-square quotes from two suppliers.
Count the steps in the flight and type the number into the Number of steps field.
Measure the Riser rise, the vertical face of one step and enter it, choosing the matching unit.
Measure the Effective tread run, the horizontal surface of one step and enter it in the same way.
If there is a landing at the top or bottom, enter its Landing depth; otherwise leave it at zero.
Enter the Stair width, measured across the tread from wall to wall or from stringer to stringer.
Choose whether the installation will include a Stair nosing overhang, Yes adds 25 mm per step.
In the Allowances section, set Extra length for pattern matching and tuck-in, and Extra width for side trimming.
Pick the Pricing basis your supplier uses, enter the Price, and read the total cost in the results panel.
The calculation treats each step as a length of carpet that must cover both its vertical face and its horizontal surface, plus any nosing wrap. That per-step length is multiplied by the step count, then extended for the landing and the extra-length allowance. Width is the stair width plus the extra-width allowance.
Formula: Per-step length = Effective Tread Run + Riser Rise + Nosing Overhang
Formula: Flight length = Number of Steps × Per-step length
Formula: Carpet Length = Flight length + Landing Depth + Extra Length
Formula: Carpet Width = Stair Width + Extra Width
Formula: Carpet Area = Carpet Length × Carpet Width
Formula: Total Cost = Price × Area (or Price × Length, for linear pricing)
Nosing overhang is applied at 25 mm per step when the toggle is set to Yes. The step count must be greater than zero, and riser, tread and stair width must all be positive; otherwise the results panel shows an invalid-input message rather than a partial figure. Landing depth and both allowances default to zero if left blank or negative, so omitting them simply removes them from the total.
A homeowner is carpeting a straight flight of 12 steps. Each riser is 18 cm, each tread is 27 cm, and the stair width is 88 cm. There is no landing, the nosing will be wrapped, and the fitter wants 12 cm extra length and 6 cm extra width. Carpet is priced at $28 per square yard.
Per-step length = 0.27 + 0.18 + 0.025 = 0.475 m
Flight length = 12 × 0.475 = 5.70 m
Carpet length = 5.70 + 0 + 0.12 = 5.82 m
Carpet width = 0.88 + 0.06 = 0.94 m
Carpet area = 5.82 × 0.94 = 5.471 m²
Area in square yards = 5.471 ÷ 0.83612736 = 6.54 yd²
Area in square feet = 5.471 ÷ 0.09290304 = 58.9 ft²
Total cost = 6.54 × $28 = **$183.12**
The takeaway: a 12-step flight consumes roughly 6.5 square yards of carpet once the nosing wrap and allowances are included. Without the nosing overhang the per-step length drops to 0.45 m and the area falls to about 6.2 square yards, a difference of a third of a square yard, which matters more on longer flights and wider stairs.
A room is a flat rectangle, so area equals length times width. A staircase is a folded surface: every step has a horizontal tread and a vertical riser, and the carpet has to cover both in one continuous run. That means the effective length of each step is roughly the tread plus the riser, not just the tread. Once a nosing wrap is added, the per-step figure grows again. Treating a staircase as a flat area underestimates the carpet by 40–60%, depending on the riser-to-tread ratio.
Measure the riser height and the tread depth of one step, plus the width across the stairs. Count the steps. If you plan to wrap the nosing, add 25 mm to the tread measurement. Enter those figures into the calculator and it will produce the total carpet length, width and area.
Yes. Carpet runs continuously down the riser, across the tread and over the nosing, so each step consumes tread plus riser plus any nosing wrap. Measuring only the tread typically underestimates the carpet by 40% or more.
Around 25 mm (1 inch) per step is the common allowance for wrapping the front edge of the tread. Some installations use a smaller figure if the nosing is particularly shallow or if a gripper rod already covers the edge. The calculator uses 25 mm when the nosing toggle is set to Yes.
Twelve to fifteen percent on top of the calculated area is a sensible starting point. Plain textures with no pattern may need only 5–10%, while striped or geometric carpets that must align across steps can need 15% or more. The calculator lets you enter extra length and width directly, which is often more precise than a flat percentage.
Yes. Enter the landing depth in the field provided. The landing depth is added to the flight length and then multiplied by the carpet width. If the landing is wider than the stair, you will need to enter the wider dimension as the stair width or add the difference to the extra-width allowance.
Per-square-yard pricing multiplies the price by the total area in square yards, so the cost reflects how much carpet surface you consume. Per-linear-metre pricing multiplies the price by the length of roll you use, regardless of how wide the roll is. Fitters often quote linear because it reflects how much roll they cut from, which is why both options are included.
Carpet rolls are typically 3.66 m or 4 m wide (12 or 13.1 feet). Since a stair is rarely wider than 1.2 m, one roll width provides enough for the full staircase with material to spare, and the offcut cannot be used elsewhere. That is why a fitter may prefer to quote by linear length rather than area.
Yes. Winders, the wedge-shaped steps at a turn have a varying tread depth, so a single tread figure will not capture them accurately. Measure the deepest part of the winder tread and use that as the effective tread run, or add a generous allowance for the extra material those steps consume.
Fully. Every length field has its own unit dropdown, including inches and feet, and the calculator converts internally to metres before multiplying. You can measure the stairs in inches and price the carpet in square yards without any manual conversion.
The calculator shows an invalid-input message and clears the results. Step count, riser, tread and stair width must all be greater than zero. Landing depth and the extra allowances are optional and are treated as zero if left blank.
No. The calculation covers the carpet only. Underlay, gripper rods, door bars and any stair rods are separate items and should be priced independently. Underlay for a staircase is typically sold in the same area unit as the carpet.
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