Skip to main content
lab.golamrabbani.org

Staircase Calculator

Riser height, tread depth, total run, and stringer length from total rise.

Written by Golam Rabbani, Founder & Lead Engineer

Units:
Units

Floor-to-floor vertical height

IRC minimum 10"; 11" is comfortable

How to use this staircase calculator

  1. Toggle inches or centimetres.
  2. Enter the total rise: the floor-to-floor vertical height the stair must climb.
  3. Enter your desired tread depth (11″ / 28 cm is a comfortable target; IRC minimum is 10″).
  4. Press Calculate to see step count, riser height, total run, and stringer length.
  5. A green or red message confirms whether the result meets typical IRC residential limits.

About this staircase calculator

The staircase calculator works out the geometry of a straight residential stair from one input: the total rise (floor-to-floor distance). It chooses a step count that keeps each riser at or below the IRC R311.7 maximum of 7-3/4 inches, while staying as close as possible to the 7-inch comfort target. From there it returns the per-riser height, the per-tread depth, the total horizontal run, and the stringer length using the Pythagorean formula √(rise² + run²).

Worked example: a total rise of 108 inches (9 ft, a typical first-to-second-floor distance with finished floors). The calculator picks 15 risers (108 ÷ 15 = 7.20″, well inside the 7.75″ limit). With 15 risers there are 14 treads. At an 11″ tread depth, the total run is 14 × 11 = 154 inches. Stringer length = √(108² + 154²) = √(11664 + 23716) = √35380 ≈ 188.1 inches (15.67 ft). You would order 16-foot 2×12 stringers and trim to fit.

Two well-known rules apply: 2 × riser + tread ≈ 25 (the 'comfort equation'), and the total run plus 36-inch landing must fit your floor plan. For commercial stairs, allowable risers and treads differ — IBC limits a commercial riser to 7″ and requires an 11″ tread. The calculator is configured for residential IRC limits; check the applicable code for your project before cutting stringers.

FAQ

What is the maximum riser height by code?
7-3/4 inches (197 mm) for residential stairs in the US IRC R311.7. International Building Code limits commercial stairs to 7 inches (178 mm). Most countries are within ±10 mm of these values.
What is the minimum tread depth?
IRC requires 10″ (254 mm) minimum residential. IBC requires 11″ commercial. Comfortable home stairs are 11–12″.
Why does the calculator pick a specific step count?
It picks the smallest number of risers that keeps each one at or below 7.75″ while staying as close to 7″ as possible. Fewer steps would exceed code; more steps would needlessly increase the run.
How long should my stringer board be?
The calculator returns the diagonal length. Add ~6–12 inches for top and bottom plumb cuts when ordering stock. A 9-ft-rise stair usually needs 16-ft 2×12 stringers.
Does this account for nosing or stair width?
No — it returns rise/run geometry only. Nosing (the lip overhang) is typically 0.75″–1.25″. Stair width per IRC must be at least 36 inches minus handrails.
Is the calculator free?
Yes — free, no signup, runs in your browser.