Stair Carpet Calculator

How to use this stair carpet calculator

What this calculator does. It estimates the continuous carpet dimensions needed to cover a straight stair flight, its optional landing, and a shaped nosing overhang. It also converts those dimensions into area and a material-only cost. Use it for early purchasing, comparing a full-width carpet with a runner, checking a supplier quote, or testing how a larger allowance affects the order. It does not design the stair, verify building-code compliance, determine installation labor, or account automatically for patterned-carpet repeats, seams, winders, curved stairs, or waste imposed by a specific roll width.

How to calculate. The calculator opens with a complete metric demonstration and an immediately available XLSX workbook. Follow these steps:

1. Select Measurement system. Metric uses centimeters for entries and square meters for area; imperial uses inches and square feet. Switching systems converts the values already entered.
2. Enter Number of steps, Riser rise, Effective tread run, Landing depth, and Stair width. Measure finished surfaces rather than relying only on nominal plans.
3. Choose With stair nosing overhang?. When Yes, select Nosing shape and enter Nosing overhang plus Nosing thickness. The shape changes the exposed perimeter that the carpet wraps.
4. Add Extra length and Extra width per side. The width allowance is doubled because it applies to both edges. Enter Carpet price in dollars per displayed area unit.
5. Read Carpet length, Carpet width, Carpet area, Flight coverage before landing, and Estimated carpet cost. The table shows how risers, nosings, treads, landing, and allowance combine.
6. Use Download Excel to save the current typed inputs and results. Reset clears the demonstration and calculated state; Excel remains unavailable until a complete valid set is entered again.

Input guide. Number of steps is a required whole number from 1 to 200; 4 is the example. Increasing it adds one riser/nosing section per step and one tread for every step after the first. Riser rise and Effective tread run are required positive dimensions; the example uses 18 cm and 25 cm. A common mistake is measuring the tread's visible top rather than the effective riser-to-riser run. Landing depth is required but may be zero; 100 cm is shown. Stair width must be positive; the example is 100 cm. With stair nosing overhang? controls whether nosing geometry applies. For a rounded edge, the example uses a 2.5 cm Nosing overhang and 2 cm Nosing thickness; overhang must be large enough for the selected geometry. Rectangular and triangular options use different exposed-perimeter equations. Extra length and Extra width per side accept zero or positive values; 10 cm and 1 cm are realistic small allowances. Carpet price accepts zero or a positive decimal; $32/m² is the example. Do not enter currency symbols, thousands separators, percentages, or scientific notation.

Output guide and worked example. Flight coverage before landing is the sum of all vertical/nosing wraps and the treads. For the rounded example, one vertical/nosing section is 18 – 2 + 2 × (2.5 – 1) + π × 2 ÷ 2 = 22.1416 cm. Four such sections plus three 25 cm treads equal 163.5664 cm. Adding the 100 cm landing and 10 cm allowance gives Carpet length 273.57 cm, displayed as 2.74 m. Adding 1 cm to each side of a 100 cm stair gives Carpet width 102 cm, or 1.02 m. Their product gives Carpet area 2.7904 m², displayed as 2.79 m². At $32/m², Estimated carpet cost is $89.29. These are planning estimates, not a supplier cutting schedule.

For measurement context, review the U.S. Occupational Safety and Health Administration's stairway dimensional requirements and the National Institute of Standards and Technology guide to SI length units. These references help distinguish stair geometry and unit conventions from the carpet-order estimate.