01
Formula
Risers = round(total rise ÷ target riser).
Riser height = total rise ÷ risers. Treads = risers − 1. Run = treads × tread depth. Stringer = square root of (rise² + run²). All of those inputs are in inches.
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Stair calculator for rise, run, and stringers
This stair calculator splits a total rise into equal risers and a straight run of treads. It is a planning layout, not a determination that the stair meets a building code.
Risers
14at 7.71 in
Treads13
Total run130.00 in
Stringer length169.01 in
2R + T25.43 in (Outside 24–25 in)
Planning layout only, not a building-code determination. Confirm rise, run, headroom and guards with the code that applies to the job.
How it works
Round the riser count, then divide the rise equally.
Divide the total rise by the target riser and round to the nearest whole number of risers, at least one. Each riser is the total rise divided by that count, so the steps are equal. Treads are one fewer than risers on a straight run from a floor to a floor. Total run is treads times the tread depth you enter. Stringer length is the hypotenuse of the rise and the run. The Blondel check is 2 × riser + tread. A common comfort band is 24 to 25 inches. Landing outside that band does not by itself make a stair illegal or legal.
02
Example
A 108 inch rise, 7.5 inch target, 10 inch treads.
108 ÷ 7.5 is 14.4, which rounds to 14 risers. Each riser is 7.71 inches. There are 13 treads and 130 inches of run. The stringer is 169.01 inches. 2R + T is 25.43 inches, just outside the 24–25 band. Try a different target if you want that check inside the band.
03
Tips
Headroom, landings, and guards are not in the math.
Residential codes often limit riser height and require a minimum tread, but the limit depends on the code adopted where the stair is built. Measure the finished floor to finished floor, including the flooring. A nosing changes the going. This page does not draw the nosing.
04
Equipment
Stairs are one part of a job site.
If the business is buying construction equipment to build the work around the stair, Dengaro can take an application from $15,000 to $2 million. The stair layout is not a loan amount.
Important questions
Know what to expect.
How does the stair calculator choose the number of risers?+
It divides the total rise by your target riser and rounds to the nearest whole riser. You can change the target to land on a different count. The risers then share the rise exactly.
Why are there fewer treads than risers?+
On a straight flight between two floors, the top riser lands on the upper floor, so that step does not need a tread in the run. A different layout, such as a landing in the middle, needs a separate run.
What is 2R + T?+
Twice the riser height plus the tread depth, in inches. Many carpenters look for a result near 24 to 25. It is a comfort rule of thumb, not a code citation.
Can I use this for deck stairs?+
Yes, if you enter the total rise from the landing to the deck surface and design one straight run. Codes for exterior stairs can differ from interior stairs. Confirm locally.
Financing built into the sale