Stair Calculator — Rise, Run & Stringer Design
Design code-compliant stairs instantly. Enter the total rise and get riser height, tread depth, total run, stringer length, and IRC compliance checks.
IRC Code: Max riser 7.75", min tread 10", max nosing 1.25". Comfort rule: riser + tread = 17-18".
How to Design Code-Compliant Footprints
Stair design starts with total rise — the vertical distance from finished floor to finished floor. The International Residential Code (IRC) establishes strict requirements for residential stairs: maximum riser height of 7-3/4", minimum tread depth of 10", and maximum nosing projection of 1-1/4".
To calculate the number of risers, divide the total rise (in inches) by your target riser height — 7" is ideal for comfort. Round to the nearest whole number, then divide the total rise by that number to get the exact riser height. The number of treads is always one fewer than the number of risers.
Stringer Calculation
The stringer is the diagonal structural member that supports the steps. Its length is calculated using the Pythagorean theorem: stringer length = sqrt(total rise² + total run²). Always add 12-18 inches to your stringer lumber for the top and bottom cuts. Most residential stringers are cut from 2×12 lumber.
Frequently Asked Questions
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