Stair Calculator

Calculate stair dimensions, riser and tread counts, stringer length, and material quantities from floor-to-floor height.

Total Rise
inches

Total vertical distance from finished floor to finished floor (9 ft = 108 in)

inches

Comfortable target: 7 in. IRC max: 7.75 in.

Tread & Width
inches

IRC minimum: 10 in. Comfortable: 11 in.

inches

IRC minimum: 36 in. 3 stringers for 36 in, 4 for 48 in

Results

Risers
15

Each 7.2" tall

Treads
14

11" deep each

Total Run
12.83 ft

154" horizontal

Stringer Length
15.67 ft

188.1" diagonal

Stair Angle
35°

Within comfortable range

Stringers Needed
3

For 36" width

2x12 Boards
4

12 ft boards for stringers

Frequently Asked Questions

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How It Works

  1. 1. Measure Total Rise

    Measure the floor-to-floor height in inches. This is the vertical distance from the surface of the lower finished floor to the surface of the upper finished floor. For a standard 9-foot ceiling with typical floor construction, this is usually about 108 inches.

  2. 2. Calculate Riser Count

    The calculator divides total rise by your target riser height (default 7 inches) and rounds to the nearest whole number. It then recalculates the exact riser height by dividing the total rise evenly among all risers, ensuring uniform steps.

  3. 3. Determine Treads and Run

    The number of treads is always one less than the number of risers (the top “tread” is the upper floor itself). Total horizontal run equals treads times tread depth. This tells you how much floor space the staircase needs.

  4. 4. Calculate Stringer Length

    Using the Pythagorean theorem (diagonal = sqrt of rise² + run²), the calculator determines the length of each stringer. This is the length of 2x12 lumber you need to cut each stringer from.

  5. 5. Check Code Compliance

    The calculator checks your stairs against IRC residential code limits: max riser height (7.75″), min tread depth (10″), and comfortable angle (under 42°). Warnings alert you to any values that may not meet code requirements.

Rule of Comfort

A well-designed stair follows the “rule of comfort”: riser height + tread depth should equal approximately 17-18 inches. With the default values of 7″ risers and 11″ treads, you get 18″ — right in the comfort zone. Adjusting one dimension affects the feel of the stairs significantly.

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Stair Calculator - Risers, Treads & Stringer Length | ConstructCalculators