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Stair Carpet Calculator

How much carpet or runner a stair needs, worked out from the stair itself: every tread, every riser, and the allowances you or your installer choose.

Your stair

Units
Usually treads + 1 (the upper floor is the top step).
The full stair width for wall-to-wall, or the runner width.
Allowances
For example, wrapping under each nosing. Ask your installer.
Top and bottom tuck or overlap.

Carpet length 21 ft 5 1/2 in (23 ft 7 1/4 in with waste), area 64.4 sq ft (7.15 sq yd). Results and details

Worked example: edit any value

Carpet needed

Covered length 21 ft 5 1/2 in
With waste 23 ft 7 1/4 in
Area 64.4 sq ft (7.15 sq yd)
Area with waste 70.8 sq ft (7.87 sq yd)

Per step ≈ 19 3/16 in

Covered length follows the profile: every tread (including its nosing) and every riser face. Installers add their own allowances for seams, pattern repeat and the wrap style; ask yours before ordering.

Carpet length per stepEach step needs the tread depth (11 1/2 in) plus the riser height (7 11/16 in) of carpet.tread 11 1/2 inriser 7 11/16 incarpet followsevery tread and riser
The carpet follows every tread, including the nosing, and every riser face.
How this result was calculated
  1. Length along the stairT × (d + extra) + R × h + ends = 13 × (11.5 + 0) + 14 × 7.7143 + 0 = 257.5 inR × h is simply the total rise, a useful cross-check.
  2. With waste257.5 × 1.1 = 283.25 in
  3. Arealength × width = 257.5 × 36 → 64.4 sq ft (7.15 sq yd)
All values (table)
ItemValueNote
Treads / risers13 / 14
Per step≈ 19 3/16 intread depth + riser + extra
Covered length21 ft 5 1/2 in
With 10 % waste23 ft 7 1/4 in
Width36 inrunner or full stair width
Area64.4 sq ft (7.15 sq yd)
Area with 10 % waste70.8 sq ft (7.87 sq yd)

How carpet length is worked out

Carpet on a stair follows its profile: across each tread, including the rounded nosing, then down the face of each riser. So the covered length is treads × tread depth + risers × riser height. The risers part is simply the total rise, which makes a quick cross-check. Measure the tread depth front to back including the nosing, which is deeper than the going a stair calculator uses.

Two styles change how much goes around each step: a waterfall drops straight from the nosing to the next tread, while a Hollywood or cap-and-band install wraps tightly under each nosing. Enter that wrap as "extra per step", and any tuck at the top and bottom as "extra at the ends". Ask your installer for their allowances; seams, roll width and pattern repeat are theirs to plan.

Worked example

The 9 ft stair from the stair calculator: 13 treads 11 1/2 in deep, 14 risers of 7.714 in.

  • Length = 13 × 11.5 + 14 × 7.714 = 149.5 + 108 = 257 1/2 in (21 ft 5 1/2 in).
  • Full width, 36 in: 257.5 × 36 = 9,270 sq in = 64.4 sq ft (7.15 sq yd).
  • With 10 % waste: 283 1/4 in of length, 70.8 sq ft.

These are automated test fixtures (carpet C1 and the allowance test).

Carpet and stair safety

Codes measure risers and treads without carpet (IRC 2024 R318.7.5), but thick pad and carpet still change how a stair feels underfoot, especially at the nosing. Carpet must be firmly fixed at every step: loose carpet on stairs is a trip hazard.

Questions people ask

These are questions Google showed under "People also ask" for related searches (checked 2026-10-24), answered here with the same tested formulas the calculators use.

How much carpet do you need for 14 stairs?

For a typical stair with 14 risers of about 7 3/4 in and 13 treads 11 1/2 in deep (including the nosing), the carpet has to cover 13 × 11.5 + 14 × 7.71 = 257 1/2 in (21 ft 5 1/2 in) of length. At 36 in wide that is about 64 sq ft (7.2 sq yd), before waste and installer allowances. Measure your own treads and risers and enter them above.