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Staircase Calculator

Compute rise, run, angle, and number of steps for building code-compliant stairs.

Stair Dimensions

Vertical distance from finished floor to finished floor above.
Horizontal depth of each step. IRC minimum: 10 in.
IRC minimum: 80 in (6'-8").

How It Works

Calculation Method
  1. Number of risers = total rise ÷ ideal riser height (7 in / 178 mm), rounded to nearest whole number
  2. Riser height = total rise ÷ number of risers
  3. Number of treads = number of risers − 1 (the top floor acts as the final step)
  4. Total run = number of treads × tread depth
  5. Stair angle = arctan(riser height ÷ tread depth)
  6. Stringer length = √(total rise² + total run²)
IRC Building Code Requirements
RequirementIRC Standard
Maximum riser height7-3/4 in (196 mm)
Minimum tread depth10 in (254 mm)
Minimum headroom6 ft 8 in (2032 mm)
Minimum stair width36 in (914 mm)
Handrail height34–38 in (864–965 mm)
Max riser variation3/8 in (9.5 mm) between any two risers
The 7-11 Rule

A widely used guideline for comfortable stairs is a 7-inch rise and 11-inch run. Two common comfort formulas:

  • Rise + Run = 17–18 in (ideal sum for comfort)
  • 2 × Rise + Run = 24–25 in (French ergonomic formula)
Tips
  • Measure total rise from finished floor to finished floor (include flooring thickness)
  • Steeper stairs (over 40°) feel uncomfortable and may not meet code
  • The ideal stair angle is between 30° and 37°
  • For deck stairs or outdoor applications, the same IRC rules apply
  • Always verify local building codes — some jurisdictions have stricter requirements

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