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Stair Calculator

Enter the total rise and tread depth to get the number of steps, exact riser height, total run, stringer length and stair angle, with a drawing of the profile and checks against the International Residential Code (7¾" maximum riser, 10" minimum tread).

Updated November 4, 2026. Free, no sign-up; everything runs in your browser and nothing you type is stored.

Stair calculator

–Steps
–Riser height
–Total run
–Stair angle
–Stair stringer length
–2 × riser + tread

IRC residential code checks

    Stair stringer calculator: how it works

    1. Number of risers = total rise ÷ maximum riser height, rounded up. 108" ÷ 7.75" = 13.9 → 14 risers.
    2. Exact riser height = total rise ÷ risers = 108 ÷ 14 = 7.714". Every riser must be within 3/8" of the others.
    3. Treads = risers − 1 (the top floor is the last step). Total run = treads × tread depth.
    4. Stringer length = √(rise² + run²), the hypotenuse; buy lumber at least a foot longer for cuts.

    2021/2024 IRC stair rules (one- and two-family homes)

    RuleRequirement
    Maximum riser height7¾ inches
    Minimum tread depth10 inches
    Variation between stepsNo more than ⅜ inch
    HeadroomAt least 6 ft 8 in
    WidthAt least 36 inches
    Nosing¾" to 1¼" when treads are less than 11"

    Local codes can differ and commercial stairs follow the IBC (7" maximum riser, 11" minimum tread). Check with your building department before you build.

    Common questions

    How do I calculate the number of stairs?

    Divide the total rise by 7.75 inches and round up. A 9-foot (108-inch) rise needs 14 risers of 7.71 inches.

    How long is a stair stringer?

    Use the Pythagorean theorem: √(total rise² + total run²). For 108" of rise and 136.5" of run, about 174", so a 16-foot board.

    What is the maximum stair riser height?

    7¾ inches under the International Residential Code, with treads at least 10 inches deep.

    What angle should stairs be?

    Most residential stairs end up between about 30° and 37°. The IRC limits set a maximum of about 37.8°.

    How many stairs for an 8-foot ceiling?

    With a 9-foot floor-to-floor rise (8-foot ceiling plus floor framing), 14 risers. Measure your actual rise, finished floor to finished floor.

    Sources

    Related

    General information, not financial, tax or legal advice. Check important numbers with the official source before acting on them.