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Staircase Calculator

Calculates stair dimensions (rise, run, treads) compliant with IRC code. Includes comfort ratio, stringer length, and code compliance check.

9 ft = 108 in. Measure from finished floor to finished floor.

IRC minimum: 10 inches (nosing to nosing)

IRC minimum: 36 inches clear

Results

Number of Treads
--
Riser Height
--
Total Run
--
Stringer Length
--
Comfort Ratio (2R+T)
--
Target: 24-25 inches
Stair Angle
--
IRC Compliant
--

Based on IRC R311.7 residential stair requirements. Always verify with local building codes, which may be more restrictive.

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How to Use This Calculator

1. Measure total rise. This is the vertical distance from finished floor to finished floor, measured in inches. A 9-foot ceiling typically results in about 108 inches of total rise (accounting for floor framing and subfloor above).

2. Set tread depth. The IRC minimum is 10 inches from nosing to nosing. The calculator uses the comfort formula (2R + T = 24-25") to recommend ideal tread depth.

3. Enter stair width. IRC minimum is 36 inches clear width. Wider stairs are more comfortable and may be required in some jurisdictions.

4. Check code compliance. The calculator flags any dimensions that violate IRC R311.7 requirements.

How the Formula Works

Number_of_Risers = CEIL(Total_Rise / 7.75)

Actual_Riser = Total_Rise / Number_of_Risers

Total_Run = (Risers - 1) x Tread_Depth

Stringer = SQRT(Total_Rise^2 + Total_Run^2)

Comfort = 2 x Riser + Tread (target 24-25")

The number of risers is always one more than the number of treads (the top floor acts as the final tread). The stringer length is calculated using the Pythagorean theorem.

Frequently Asked Questions

What is the IRC code for stairs?
IRC R311.7 requires a maximum riser height of 7-3/4 inches, minimum tread depth of 10 inches, and no more than 3/8 inch variation between risers or treads. Minimum width is 36 inches clear.
How do I calculate stair rise and run?
Divide the total rise (floor to floor in inches) by 7.75 to get the minimum number of risers. Round up. Then divide the total rise by the number of risers for actual riser height.
What is the ideal stair riser height?
The ideal riser height is between 7 and 7.5 inches. The comfort formula 2R + T should equal 24-25 inches for optimal comfort.

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