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Stair Calculator

Calculate riser count, tread count, total run, and approximate stringer length from total rise and target riser height. One shared length unit for all stair dimensions. Basic geometry only — verify local code.

Stair diagram showing rise and runTotal riseTotal run

All stair lengths share one unit. Changing the unit converts values so inches are never read as feet.

Parsed value: 108

Parsed value: 7

Parsed value: 10

Assumptions

  • Straight flight with uniform risers and treads.
  • Target riser near 7 in (≈178 mm) is common in US residential work.
  • Does not verify IRC or local code compliance.
  • Landing platforms and headroom are not calculated.
  • Total rise is floor-to-floor vertical distance.
  • Stair width is optional and informational only.
Formula
Number of risers = ceil(total rise ÷ target riser height). Actual riser = total rise ÷ risers. Treads = risers − 1. Total run = treads × tread depth. Stringer ≈ √(rise² + run²). All lengths use your selected unit (converted via meters/inches internally).

9 ft total rise, 7 in target riser

  1. Enter total rise as 108 in (or 9 ft with unit Feet — values convert). Risers = 108 ÷ 7 ≈ 15.4 → 16 risers (ceil). Actual riser = 108 ÷ 16 = 6.75 in. Treads = 15. Run = 15 × 10 in tread = 150 in. Stringer ≈ √(108² + 150²) ≈ 184.9 in.

How to measure

Measure vertical distance from finished floor to finished floor (or landing). Enter rise, riser, and tread in the same unit — inches for framing precision, or feet/meters for whole-story heights. Switching the unit converts all fields so 108 inches never becomes 108 feet.

Common mistakes

  • Measuring to subfloor instead of finished floor height.
  • Unequal risers after adjusting only the bottom step.
  • Ignoring maximum riser height and minimum tread depth in local code.
  • Changing the length unit without converting values (this tool converts automatically).

Frequently asked questions

What is a comfortable riser height?
7–7.75 in is typical in US homes. Outdoor deck stairs often use 7–7.25 in.
Is this code-compliant?
No. Always check local building code for riser, tread, handrail, and landing rules.
What about the nosing?
Tread depth here is horizontal run. Some codes require nosing projection beyond the riser.
Split flights with a landing?
Calculate each flight separately from landing to floor.

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