Stair Carpet Calculator

To calculate the total length of carpet required for a flight of stairs, the tool evaluates the vertical rise and horizontal run of each step, plus any intermediate landings. Depending on whether your stairs feature a nosing overhang, the effective profile changes. For standard installations without nosing, the length formula is: Carpet Length = (Number of Steps × Riser Rise) + ((Number of Steps - 1) × Effective Tread Run) + Landing Depth + Extra Length Allowance. When nosing overhangs are included, the riser dimension is replaced by a specialized nosing profile calculation (such as rectangular, rounded, or triangular V-shapes) to ensure the fabric molds completely over the stair edge. Total area is found by multiplying this adjusted length by the stair width (plus width allowances), and total cost is determined by multiplying the final square footage by your price per unit area.

Let us calculate the carpet requirement and cost for a straight staircase with 12 steps and a landing. Suppose each step has a riser rise of 7 inches, an effective tread run of 10 inches, and a rectangular nosing overhang of 1 inch. The landing depth is 36 inches, the stair width is 36 inches (3 feet), and the carpet price is $5.00 per square foot. First, we compute the riser-and-overhang factor: 7 inches + (2 × 1 inch) = 9 inches. Next, we find the total carpet length: (12 steps × 9 inches) + (11 treads × 10 inches) + 36 inches = 108 + 110 + 36 = 254 inches (approximately 21.17 feet). Adding a standard 10% waste allowance brings the length to roughly 23.3 feet. Multiplying this by a carpet width of 3 feet gives approximately 70 square feet of total carpet area. At $5.00 per square foot, the estimated material cost comes out to $350.00.

Always factor in extra length and width allowances to account for pattern matching, trimming errors, and professional installation grips. If your carpet features a distinct geometric or plaid pattern, alignment across the nose of each step is critical, which may require additional yardage. Furthermore, always measure at the widest point of the stairs, particularly if you have decorative volutes, flairs, or open-ended steps at the bottom of the flight.