Stair Calculator
Calculate stair dimensions including rise, run, number of steps, and stringer length.
Result
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A stair calculator determines the number of risers and treads, stringer length, and stair angle from your floor-to-floor height to ensure code-compliant, comfortable stairs.
Examples
9-foot ceiling (108 inches)
With 7.5 in risers: 108 / 7.5 = 14.4 -> 14 risers. Actual riser: 108/14 = 7.714 in. 13 treads at 10 in = 130 in run. Stringer: sqrt(108^2 + 130^2) = 169 in (14.1 ft).
Frequently Asked Questions
What is the building code for stairs?
The International Residential Code (IRC) requires a maximum riser height of 7-3/4 inches and a minimum tread depth of 10 inches. Riser height variation must not exceed 3/8 inch between the tallest and shortest risers.
What is the rule of 17?
The rule of 17 (also called the comfort rule) states that the riser height plus tread depth should equal between 17 and 18 inches for the most comfortable staircase.
Result
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Quick Tips
- •Always verify your total rise measurement at multiple points, as floors are rarely perfectly level.
- •Use the Rule of 17 (riser + tread = 17-18 inches) as a quick comfort check before cutting stringers.
- •Purchase stringer lumber at least 2 inches longer than the calculated length to allow for trimming.