Article — Stair Carpet Calculator
Stair carpet calculator: sq yd of runner for waterfall and wrapped installs
For 13 standard residential steps with 10-inch tread and 7.5-inch riser, waterfall installation with a 27-inch runner needs about 5.2 square yards including 10% waste. Wrapped (Hollywood) install with the same dimensions needs about 5.9 sq yd. Patterned carpet and winder stairs require 15-25% waste.
Stair carpet sits in a different category from room carpet. Each step is a small panel that must match the next perfectly, the nosing edge wears faster than any flat carpet, and installation requires specialized tools. Getting the square yards right matters because partial-piece reorders almost always require a second seam, which is the most failure-prone part of a stair install.
What is stair carpet?
Stair carpet is carpet that covers stair treads and risers. Unlike room carpet, it can be installed as a full wall-to-wall covering or as a center runner that leaves the outer edges of each tread exposed. Runner installation is more common in 2025 — it shows off hardwood treads, is easier to clean at the edges, and uses less material.
Carpet width is constrained by the manufacturer's roll dimensions. Most carpet is woven in 12-foot or 15-foot wide rolls. For stair runners, the carpet is cut to a narrower width (24-36 inches typical) and the long dimension runs the length of the stair. The exposed wood edges between the runner and the stair tread typically measure 2-3 inches per side.
Stair carpet measurements
Three measurements drive the calculation. Tread depth is the horizontal distance from the back of one step to the back of the next — typically 10-11 inches in residential stairs. Riser height is the vertical distance between tread surfaces — typically 7-7.75 inches. Step count is the number of treads from bottom landing to top landing.
The linear length of carpet for one step in waterfall installation equals tread depth plus riser height. For wrapped installation, add the nosing overhang (1 inch standard). Multiply by step count to get total linear length, then by runner width to get area. Divide by 1,296 to convert square inches to square yards.
The first patented stair carpet runner clip system dates to 1875 — invented in Connecticut as a brass rod that wedged the carpet against the back of each tread. Hilton and Pullman hotels of the late 1800s standardized 27-inch runner width on luxury staircases. That width remains the most common today for the same reason — it suits a standard 36-inch wide stair with proportional margins.
Waterfall vs wrapped stair carpet
The two main installation methods produce visibly different results. Waterfall installation lets the carpet drop straight down each riser. The carpet creates a small gap at the nosing of each tread, which is where the carpet visually meets the next riser. The look is informal and the material requirement is lower.
Wrapped installation (also called Hollywood or upholstered) tucks the carpet around the front nosing of each tread before continuing down the riser. This creates a snug fit that follows the contour of the step exactly. The result is more formal, more durable at the nosing, and requires precise cutting. Wrapped install uses 5-10% more material than waterfall.
Carpet pile should run downward from the top of the stairs to the bottom. This direction matches how feet wear the carpet and produces the most uniform appearance. Installing pile-up shortens the carpet's effective lifetime by 20-30% and creates a directional shimmer that catches light differently from above and below.
Stair carpet width and runner size
Standard runner widths are 24, 27, 30, and 36 inches. The choice depends on stair width. For a 36-inch wide staircase (the IRC residential minimum), a 27 or 30-inch runner leaves 3-4.5 inches of exposed wood on each side. For a 42-inch staircase, choose 30-36 inches. For wide stairs above 48 inches, use 36-inch runner or go full wall-to-wall.
A traditional formula: runner width = stair width minus 4-6 inches, divided into equal margins. For 36-inch stair: 36 - 6 = 30-inch runner with 3-inch margins. The wood margins must be wide enough to hold their own visual weight without looking like installer error. Less than 2 inches per side looks accidental; more than 5 inches per side starts to feel narrow.
Stair carpet waste allowance
Waste varies with stair geometry and carpet pattern. Plain carpet on straight stairs with waterfall install: 10%. The same on wrapped install: 12-15%. L-shape stairs with one landing: add 5-10% for the corner cuts. Winder stairs that turn without a landing: 20-30% because each pie-shaped tread cuts unique pieces.
Patterned carpet always needs more. Geometric or floral patterns must match across seams, so any pattern repeat larger than 6 inches forces alignment cuts that consume 5-15% extra material. Stripe runners are the most demanding — alignment errors stand out from every angle, requiring 20%+ waste even on straight stairs.
Stair carpet installation cost
Professional installation in 2025-2026 averages $5-12 per step for waterfall and $8-15 per step for wrapped. A typical 13-step residential stair costs $65-160 in waterfall labor or $100-200 in wrapped labor. Add material at $30-100 per square yard (mid-grade carpet), and total cost runs $300-800 for the average residential stair.
DIY installation is feasible for waterfall but challenging for wrapped. Required tools: knee kicker ($50-100), stair tool ($30-50), staple gun, sharp utility knife, tape measure, chalk line. A capable DIYer can complete waterfall install on 13 steps in 4-6 hours. Wrapped install typically takes 8-12 hours and produces tighter results in trained hands.
Order one extra panel beyond what the calculator suggests. Stair carpet wears fastest at the nosing of each tread; the extra panel lets you replace high-wear sections later without dye-lot mismatch. Carpet dye lots vary slightly between manufacturing runs, so reorders 6+ months later rarely match exactly.
Common stair carpet mistakes
The first common mistake is undermeasuring nosing overhang. Wrapped installation needs the overhang added to every step's linear allocation, not just the bottom step. Forgetting to multiply by step count leaves you 6-12 inches short on a typical residential stair.
The second mistake is ignoring the bullnose at the top of the stair (the rounded edge where the top landing meets the stair). The bullnose typically extends 1-2 inches beyond the riser face and needs its own carpet piece. Most calculators include this in the standard wrapped overhang; if yours does not, add a 2-inch piece manually.
The third mistake is forgetting padding. Stair padding rolls in 27-inch standard width, just like runners. The pad does not need waste added (no pattern matching), but the linear length must match the carpet plus 2-3 inches per step for compression. Order pad separately at $1-3 per linear foot.
Waterfall length N × (T + R)Wrapped length N × (T + R + 1)Sq yd L_in × W_in ÷ 1,296Typical waste +10-15%Winder waste +25%Pro labor $5-12 / step- 13 steps typical residential stair (8-foot floor-to-floor)
- 10-11 inch standard tread depth
- 7-7.75 inch standard riser height
- 27 inch most common runner width
- 1 inch typical nosing overhang for wrapped install
- 5-6 sq yd typical material for a 13-step waterfall install
- 10% waste for plain carpet on straight stairs
- $5-15 / step typical installation labor cost