Stair Calculator
Plan stair rise, run, and tread depth with code-friendly guidance
About this calculator
The Stair Calculator plans an interior staircase from total rise, preferred riser height, and tread depth (inches). It computes the number of equal risers and treads, the actual riser height, total horizontal run, and stringer angle, then checks the plan against IRC residential guidance: risers 4–7.75 in, treads at least 10 in, and Blondel's rule (2 × riser + tread between 24 and 25 in). Non-positive inputs return an error.
How to use the Stair Calculator calculator
- Enter your values into the input fields.
- Read the result — it updates instantly as you type.
- Adjust the inputs to compare scenarios.
- Copy the page URL to share the exact calculation.
Common examples
- 108 in rise, 7.5 in preferred riser, 10.5 in tread → 15 risers at 7.2 in, 14 treads, run 147 in, 36.3° — all checks pass
- 112 in rise, 7 in riser, 11 in tread → 16 risers at 7 in, run 165 in, 34.2° angle
- 36 in rise (deck steps), 7.5 in riser, 10 in tread → 5 risers at 7.2 in, 4 treads, run 40 in
Frequently asked questions
How does the Stair Calculator calculator work?
Enter your numbers and the calculator applies the standard formula for this everyday task, showing the result and how it was reached. It handles the unit and rounding details so you do not have to.
When would I use the Stair Calculator calculator?
Whenever this comes up in daily life — planning, shopping, home projects, travel or work — and you want a quick, dependable answer instead of estimating or working it out by hand.
How accurate are the results?
The math runs at full precision internally and only the displayed value is rounded for readability. For real-world use the practical limit is the accuracy of the numbers you enter, not the calculation.
Can I share a specific calculation with someone else?
Yes. Every value you enter updates the URL, so copying the address bar and sharing the link reopens the exact same calculation for whoever clicks it.