Understanding Stair Carpet Installation
Carpeting a staircase requires careful measurement of vertical and horizontal distances. The riser rise is the vertical height between consecutive steps, while the effective tread run is the horizontal depth of each step. Most residential stairs have riser rises between 17–19 cm (7–7.5 inches) and tread runs of 25–28 cm (10–11 inches).
When stairs feature stair nosing—the rounded or angled edge that overhangs the riser—you must account for this extra length in your carpet calculation. Nosing adds approximately 2–5 cm to the coverage needed per step, depending on the nosing profile (rectangular, triangular, rounded, or V-shaped).
Installation typically progresses from bottom to top or top to bottom, with bottom-up being easier for first-timers since you avoid stepping over loose carpet. Most installers use:
- Tackless strips or tack boards to secure the carpet at the perimeter
- Knee kickers and power stretchers to achieve proper tension
- Staples or adhesive for securing edges along the riser face
Carpet Length and Area Formulas
The total carpet length depends on whether your stairs have nosing overhang. Account for each step's vertical rise, the horizontal tread, the landing depth, and a small allowance for measurement tolerance or joint scrunching.
Carpet Length (no nosing) = (Riser Rise × Number of Steps) + (Tread Run × (Number of Steps − 1)) + Landing Depth + Extra Length Allowance
Carpet Length (with nosing) = (Adjusted Riser Height × Number of Steps) + (Tread Run × (Number of Steps − 1)) + Landing Depth + Extra Length Allowance
Carpet Width = Stair Width + Extra Width Allowance
Carpet Area = Carpet Length × Carpet Width
Total Cost = Carpet Area × Price per Square Unit
Riser Rise— Vertical distance (in cm or inches) between two consecutive step surfacesTread Run— Horizontal depth of each step measured from riser to riserNumber of Steps— Total count of steps in the flight; each level change counts as one stepLanding Depth— Length of any intermediate landing or platform along the stair directionStair Width— Full width of the staircase measured perpendicular to the direction of travelAdjusted Riser Height— Riser rise plus the additional vertical distance added by nosing overhang, depending on nosing shapeExtra Length & Width Allowance— Buffer space (typically 5–10 cm) to account for measuring errors, seaming, and carpet movement
Accounting for Nosing Overhang
Stair nosing—the edge that protrudes beyond the riser face—increases the effective vertical height that carpet must cover. The additional length varies by nosing profile:
- Rectangular nosing: Adds twice the overhang distance to the riser rise
- Triangular nosing: Adds overhang and a diagonal component based on nosing thickness
- Rounded or bullnose nosing: Incorporates a curved path, typically requiring 10–15% more length than rectangular nosing of the same overhang
- V-shaped nosing: A hybrid calculation combining elements of triangular and other profiles
A typical nosing overhang ranges from 1.5–3 cm, and thickness from 1–3 cm. If you're unsure of your nosing dimensions, measure the horizontal projection (overhang) and the vertical thickness where the nosing meets the riser.
Estimating Carpet Cost
Stair carpet pricing is almost universally quoted per square meter or square foot. Once you know the total carpet area required, multiply by the unit price of your chosen carpet to get the material cost.
A typical residential staircase—12 steps with a 100 cm width, 20 cm riser rise, 25 cm tread run, and 2.5 cm nosing overhang—requires approximately 2.7–3 m² of carpet and may cost £60–£180 in materials alone, depending on carpet quality and regional pricing.
Budget for additional costs beyond the carpet itself:
- Underlay or padding: £3–£8 per m²
- Stair rods or metal edging: £5–£15 per step
- Professional installation labour: £20–£50 per step, or £150–£500 for a full flight
- Removal of old carpet and disposal
Economy carpets may cost £10–£20 per m², while premium or hardwearing options reach £40–£100 per m². Always factor in a 5–10% waste margin when ordering.
Common Pitfalls When Measuring and Ordering
Accurate measurements prevent costly shortcuts and material waste.
- Inconsistent Step Dimensions — Real staircases often have slight variations in riser height or tread depth, especially in older buildings. Measure the first, middle, and last step separately. If they differ by more than 1 cm, use the largest dimension to ensure your carpet fits all steps without gaps.
- Forgetting the Landing or Platform — Stairs with mid-flight landings or returns require additional carpet length. Measure the landing depth along the stair direction and include it in your total length calculation. Omitting this is one of the most common ordering errors.
- Underestimating Nosing Impact — Nosing overhang can add 10–20 cm to total carpet length on a 12–14 step flight. Always measure or confirm the nosing style (rectangular, rounded, etc.) and its overhang distance. If uncertain, add 2–3 cm per step as a buffer.
- Ignoring Width Allowance and Seaming — Carpet typically comes in fixed widths (3.66 m, 4.57 m, 5 m). If your stairs are wider than one roll, seaming is required. Add 5–10 cm to your measured stair width to account for seam overlap and minor dimensional changes due to humidity or stretching.