IRC Stair Code Requirements
| Dimension | Minimum | Maximum |
|---|---|---|
| Rise (height) | 4" | 7¾" |
| Run (depth) | 10" | — |
| Headroom | 6'8" | — |
| Width | 36" | — |
| Handrail height | 34" | 38" |
Stair Calculator
Calculate the exact rise, run, number of steps, and stringer length for any staircase. Ensures code-compliant dimensions so your stairs are safe and meet building requirements.
Stair Design Calculator
Frequently Asked Questions
What is the comfortable stair formula?
The Blondel formula: 2 × Rise + Run = 24–25 inches. With a 7" rise, the ideal run is 10–11". A 7" rise with 11" run gives 2×7+11 = 25 — perfect. This formula originated from French architect François Blondel in 1672 and matches the average human stride when climbing stairs.
How do I calculate stringer length?
Stringer length = √(Total Rise² + Total Run²). It's the hypotenuse of a right triangle formed by the total rise and total run. This is the minimum board length needed for a stringer (the angled support board). Always buy longer boards and cut to fit, accounting for notches and landing dimensions.
About the Stair Calculator
This free stair calculator helps you get accurate results instantly without needing to work through the math manually. Whether you need a quick estimate or a precise figure, having a reliable tool on hand saves time and reduces errors compared to manual calculation.
How to Use This Calculator
- Enter your values in the input fields above. Each field is labeled to guide you.
- Double-check your inputs — results are only as accurate as the numbers you enter.
- Click the Calculate button to see your result instantly.
- Use the result for your planning, budgeting, or decision-making.
Why Accurate Calculations Matter
Small errors in math calculations can compound into significant problems. A 1% miscalculation in a budget or measurement can translate to hundreds or thousands of dollars in wasted resources, or result in having to redo work entirely. This calculator uses the standard formulas and methods to give you reliable results you can trust.
Tips for Getting the Best Results
- Use consistent units throughout (all in feet, all in dollars, etc.)
- For estimates, add a 10% buffer to account for real-world variables
- Save your result by taking a screenshot or writing it down before closing the page
- For decisions involving significant money or safety, verify results with a qualified professional
Frequently Asked Questions
Is this calculator free? Yes — completely free with no account, login, or payment required. Use it as many times as you need.
How accurate are the results? This calculator uses the standard formulas for stair calculations. Results are accurate for typical use cases. For specialized or high-stakes applications, consult a professional.
Does it work on mobile? Yes. This calculator is fully responsive and works on smartphones, tablets, and desktops.