Stair Calculator
Work out a staircase from the total floor-to-floor rise. Get the number of steps, the actual riser height, total run, and stringer length, plus an IRC code and 2R+T comfort check.
Stair dimensions
How to use this calculator
1. Measure the total rise
This is the vertical distance from the lower finished floor to the upper finished floor — not just the height of the opening. Measure it accurately, because every step depends on it.
2. Set a target riser and tread
Start with a comfortable target riser height (around 7 in) and a tread depth (around 11 in). The calculator divides the rise into whole steps and reports the actual riser height it lands on.
3. Read the steps and stringer length
You get the number of risers and treads, the true riser height, the total horizontal run, and the diagonal stringer length so you can size your cut boards.
4. Check the code and comfort flags
The tool flags the result against the IRC riser and tread limits and against the 2R+T comfort rule. Treat them as a guide and confirm your local building code before cutting timber.
About stair geometry
How the steps are derived
Number of risers = total rise ÷ target riser, rounded to a whole number. Actual riser = total rise ÷ that whole number. Treads = risers − 1, total run = treads × tread depth, and the stringer length is the hypotenuse √(rise² + run²).
What are the IRC limits for stairs?
The International Residential Code caps the riser at 7.75 in (~197 mm) and requires a tread depth of at least 10 in (~254 mm). Risers across a flight should vary by no more than 0.375 in. Always confirm the code adopted by your local jurisdiction.
What is the 2R + T rule?
Twice the riser plus the tread depth should fall roughly between 24 and 25 in. It keeps the stair's rhythm comfortable: taller risers pair with shorter treads, and shorter risers with deeper treads.