Stair Calculator
Calculate rise, run, and number of treads for code-compliant stairs (IRC residential).
About This Tool
When to Use This Calculator
Use the Stair Calculator when framing new stairs, replacing existing stairs, or building a deck with steps. Proper rise and run calculations are critical for both building code compliance and comfortable, safe stairs that will not trip anyone. Even small errors in riser height get multiplied across the entire flight, creating a noticeably uneven first or last step that becomes a tripping hazard.
How It Works
Enter the total floor-to-floor height and the calculator determines the optimal number of risers and the exact rise height per step that stays within IRC residential building code limits (maximum 7-3/4" rise, minimum 10" run). It generates a side-profile SVG diagram showing the stringer layout and confirms whether your design meets code requirements for riser uniformity and tread dimensions.
Tips for Best Results
- Always measure the actual floor-to-floor height after subfloor and finish flooring are accounted for on both levels — being off by even 1/4" gets multiplied across all risers.
- All risers in a single flight must be within 3/8" of each other per the IRC, so precision matters when dividing total rise by the number of steps.
- For exterior deck stairs, remember that ground settling may change the total rise over time. Consider setting the bottom on a concrete pad for stability.
- The ideal riser-plus-tread relationship for comfortable stairs is a combined rise and run between 17" and 18" (e.g., 7-1/2" rise with 10-1/2" run).