CONSTRUCTION · FRAMING

Staircase Calculator

Calculate the number of steps, rise and run per step, stringer length, and IRC code compliance for your staircase. Enter total rise and preferred tread depth.

LAST REVIEWED · APR 24, 2026 · BY D. MARQUEZ, P.E.
You need
14 steps
Est. cost
Passes
Staircase DimensionsReset
Total riseFloor-to-floor height
in
Preferred tread run10" min per IRC code
in
Meets IRC residential staircase requirements

How the staircase calculator works

Enter the total rise (floor-to-floor height in inches) and your preferred tread run. The calculator divides the total rise by the maximum allowed riser height (7.75") to determine the minimum number of steps, then calculates the actual rise per step, total horizontal run, and stringer length using the Pythagorean theorem.

IRC staircase code requirements

  • Max riser height: 7¾" (7.75")
  • Min tread depth: 10"
  • Min width: 36" clear
  • Min headroom: 6'-8" (80")
  • Max riser variation: ⅜" between any two risers

The comfort formula

A comfortable staircase follows the rule: 2 × riser + tread = 24–25 inches. A 7" rise with an 11" tread (2×7 + 11 = 25) is widely considered the most comfortable residential stair dimension.

Methodology. Steps = ceil(Total rise ÷ 7.75"). Rise per step = Total rise ÷ Steps. Stringer length = √(Total rise² + Total run²). IRC R311.7: max riser height 7¾", min tread depth 10", max variation between risers ⅜".

Sources

  • IRC R311.7 Stairways — International Residential Code (2021)
  • Stringer calculation: Pythagorean theorem for hypotenuse
  • Standard lumber for stringers: 2×12 minimum
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Frequently asked questions

How many steps for a 9-foot ceiling? +
A 9-foot ceiling means roughly 108 inches of total rise (including floor framing). At 7.75" max rise: 108 ÷ 7.75 = 13.9, so you need 14 steps with a rise of 7.71" each.
What's the ideal rise and run for stairs? +
The sweet spot is 7" rise × 11" run. This satisfies the comfort formula (2×7 + 11 = 25) and easily meets IRC code. Most people find stairs in the 7"–7.5" rise range most comfortable.
How long does a stringer need to be? +
Use the Pythagorean theorem: √(total rise² + total run²). For a 108" rise with 13 treads at 11" run (143" total run): √(108² + 143²) = √(11664 + 20449) = √32113 ≈ 179.2 inches, or about 15 feet.
Can I use 2×10 lumber for stair stringers? +
No — IRC requires a minimum 3.5" of material remaining above and below the notch cuts. With standard 7×10 notches, you need a 2×12 (11.25" actual width) to maintain structural integrity.