Stair Calculator
Calculate stair dimensions including rise, run, number of steps, and stringer length.
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)
Frequently Asked Questions
What is the building code for stairs?
What is the rule of 17?
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.
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.
How to Use This Calculator
Enter the total vertical rise (floor-to-floor height in inches), your desired riser height, and tread depth. The calculator determines the number of risers and treads, stringer length, stair angle, and code compliance.
Understanding the Formula
Risers = Total Rise / Riser Height (rounded). Treads = Risers - 1. Stringer = sqrt(Rise^2 + Run^2). Angle = atan(Rise / Run). Comfort Rule: Riser + Tread should equal 17 to 18 inches.
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.
Assumptions & Limitations
- Assumes uniform riser height across all steps; actual construction may require minor adjustments for the top or bottom riser.
- Code compliance is checked against the International Residential Code (IRC); local codes may differ.
- Does not account for headroom clearance, landing requirements, or handrail specifications.