Stair Calculator — Rise, Run & Stringers
Lay out a staircase from one measurement. Enter the total rise from floor to floor, and get the number of steps, riser height, tread depth, total run, stringer length and angle, checked against common residential code limits.
Number of risers
How to calculate stairs
- Measure the total rise from the finished lower floor to the finished upper floor.
- Enter your preferred riser height and tread run. 7–7.5 inch risers and 10–11 inch treads are comfortable.
- Read the number of risers, the exact riser height, total run and stringer length.
Stair layout basics
The total rise is divided into equal risers; every riser must be the same height (codes typically allow no more than 3/8 inch variation) or people will trip. The number of treads is one fewer than the number of risers when the top step is the upper floor itself.
Comfort follows the classic rule that two risers plus one tread should total about 24–25 inches. The International Residential Code (IRC) generally limits risers to 7¾ inches and requires treads of at least 10 inches, with nosing between ¾ and 1¼ inches on solid risers; local codes vary, so check yours.
Stringer length is the diagonal of the total rise and run. Buy stringer stock at least a foot longer than calculated to allow for cuts at the top and bottom. Remember to subtract the tread thickness from the first riser when cutting stringers, and confirm headroom (typically at least 6 ft 8 in).
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Frequently asked questions
What is the maximum stair riser height?
The IRC allows up to 7¾ inches for homes; commercial codes typically allow 7 inches. Check your local code.
What is the minimum tread depth?
Usually 10 inches under the IRC and 11 inches in commercial buildings.
How many steps for a 9 ft rise?
A 108-inch rise works out to 15 risers of 7.2 inches, with 14 treads.
Do I need a permit?
Often, especially for new stairs or decks. Check with your building department.