What Is the Stair Calculator?
Our free standard stair calculator helps you determine the correct rise height, tread depth, stringer length, and stair angle for a straight-flight staircase. Whether you're a homeowner planning a renovation or a contractor bidding a new build, getting your stair dimensions right the first time saves material costs and ensures building code compliance.
How to Use This Calculator
- Enter the total rise - the vertical distance from the finished lower floor to the finished upper floor.
- Input the desired tread depth (run). The IRC recommends a minimum of 10 inches for residential stairs.
- Review the calculated number of risers, individual riser height, stringer length, and stair angle.
- Export your results as a PDF to share with inspectors or include in your project documentation.
Why Accurate Stair Calculations Matter
Incorrectly sized stairs are one of the most common causes of trip-and-fall injuries in residential buildings. The International Residential Code (IRC) Section R311.7 mandates a maximum riser height of 7¾ inches and minimum tread depth of 10 inches. Using a stair calculator ensures every step is uniform, which is critical because even a ¼-inch variance between risers can cause stumbles.
Building Code References
Related Tools
Frequently Asked Questions
What is the ideal riser height for residential stairs?+
The ideal riser height is between 7 and 7½ inches. The IRC allows a maximum of 7¾ inches, but most builders target 7¼ inches for optimal comfort using the 2R+T ≈ 25 rule.
How do I calculate the number of steps I need?+
Divide your total rise (floor-to-floor height in inches) by your target riser height. For example, 108 inches ÷ 7.5 inches = 14.4, so you'd use either 14 or 15 risers and recalculate the exact riser height.
What is the 2R+T rule?+
The 2R+T rule states that two times the riser height plus the tread depth should equal approximately 24 to 25 inches for comfortable stair proportions. This formula has been used by builders for centuries.