Stair Stringer Calculator
Calculate stringer dimensions: total rise, number of steps, rise per step, run per step, stringer length, and cut angle. Includes an interactive SVG diagram.
How It Works
This calculator determines the optimal stringer layout based on your total rise (floor-to-floor height) and desired run per step. It calculates the number of risers needed to stay within IRC code limits (max 7.75" rise per step), the exact rise per step, total run, stringer length using the Pythagorean theorem, and the cut angle. The stringer board must be long enough to accommodate the hypotenuse of the total rise and total run, plus extra for the top and bottom connections.
Frequently Asked Questions
What is the maximum rise per step allowed by code?
The IRC (International Residential Code) 2018 allows a maximum riser height of 7-3/4 inches (7.75") and a minimum of 4 inches. The ideal riser height is between 7" and 7.5" for comfort.
How thick should a stair stringer be?
Stair stringers are typically cut from 2x12 lumber. After cutting the notches, there should be at least 3.5 inches of wood remaining at the narrowest point (the throat) for structural integrity.
How do I calculate the stringer length?
Stringer length = √(total rise² + total run²). This gives you the hypotenuse. Add 12-18 inches extra for the top and bottom connections to the framing.
How many stringers do I need?
For stairs up to 36" wide, use 3 stringers (one on each side, one center). For wider stairs, add a center stringer every 16" of width. Building codes typically require stringers no more than 16" apart.