Stair Calculator
Enter total rise (floor-to-floor height) and get step count, riser height, tread depth, total run, and stringer length. Common comfort ranges shown for reference — verify against your local building code.
Materials Needed
How stair math works
Step count is total rise divided by target riser height, rounded to a whole number. Actual riser height is then total rise ÷ step count — it will rarely equal your target exactly because it has to divide evenly. Total run is step count minus 1 (there's no tread on the top landing) multiplied by tread depth. Stringer length is the hypotenuse: √(rise² + run²).
Common comfort ranges (verify your local code)
The most-cited residential rules of thumb: riser 7–7¾", tread 10–11½", 2R+T = 24–25" as an ergonomic guideline. IRC (International Residential Code) commonly cited as max 7¾" riser and min 10" tread for residential. Commercial codes are stricter. Uniformity matters more than the exact number — every step in a flight must be within 3/8" of every other step or people trip.
This calculator does not verify code compliance. Codes vary by jurisdiction, use type (residential vs. commercial), and code adoption year. Check with your local building department or a licensed contractor before construction.
What's not included
Landings, headroom clearance, handrail requirements, nosing dimensions, stringer material selection or span, structural attachment. Geometry only.