Rise & Run Calculator
Calculate optimal rise and run from total height and horizontal space. Shows IRC 2018 code compliance for residential stairs.
How It Works
Enter your total rise (floor-to-floor height) and optionally your available horizontal space. The calculator determines the optimal number of steps, rise per step, and run per step that comply with the IRC 2018 residential building code. It checks: maximum riser height (7.75"), minimum tread depth (10"), the 2R + T comfort rule (should equal 24-25"), and maximum riser variation (3/8" between any two risers). A green/red indicator shows whether your stair design passes code.
Frequently Asked Questions
What is the 2R + T rule?
The 2R + T rule (also called the comfort rule) states that 2 × riser height + tread depth should equal approximately 24-25 inches. For example, a 7" rise + 11" tread: 2(7) + 11 = 25". This produces the most comfortable stair to walk on.
What are the IRC 2018 stair code requirements?
IRC 2018 requires: max riser height 7-3/4", min riser height 4", min tread depth 10" (nosing to nosing), min width 36", min headroom 6'8", max variation between risers 3/8", and handrails 34-38" above the nosing.
How do I measure total rise?
Measure from the finished floor surface at the bottom to the finished floor surface at the top. Include any flooring thickness that hasn't been installed yet. Accuracy is critical — even 1/4" error gets divided across all steps.