Stair Calculator (Rise and Run)
Enter the total rise from finished floor to finished floor, the largest riser you want to allow and your tread depth.
How it works
Number of risers = total rise ÷ maximum riser height, rounded up to a whole number. Riser height = total rise ÷ number of risers. Treads = risers − 1 (the top floor acts as the last step). Total run = treads × tread depth. Stringer length ≈ √(total rise² + total run²). Angle = arctan(riser ÷ tread).
Worked example: Curtis Lumber's guide: a 104 in rise with an 8¼ in maximum riser needs 13 risers of 8 in and 12 treads; at 9 in per tread the run is 108 in. SREB's example: a 70½ in rise gives 10 risers of 7.05 in.
Assumptions
- Straight stair with equal risers and treads, measured between finished floor surfaces. Nosing, riser board thickness and landings are not included; Curtis Lumber's guide adds about 2¼ in to total run for nosing and riser thickness.
- General information only: the model 2021 International Residential Code (R311.7.5), as quoted by Placer County, CA, lists a 7¾ in maximum riser and a 10 in minimum tread. Those are the defaults here, but adopted codes and amendments differ by location (Curtis Lumber's example uses New York State's 8¼ in and 9 in). Check your local building department.
- This does not check headroom, handrails, guards, width or landings. Get a permit and inspection where required.
Frequently asked questions
How do I calculate the number of stair risers?
Divide the total rise by the largest riser height you will allow and round up. Curtis Lumber's example: 104 in ÷ 8.25 in = 12.6, so 13 risers of exactly 8 in.
How many treads does a staircase have?
Usually one fewer than the number of risers in a straight flight, because the upper floor is the last step. 13 risers means 12 treads.
What riser height and tread depth are common?
As general information, the model International Residential Code lists a 7¾ in maximum riser and 10 in minimum tread; SREB's carpentry lesson describes a normal stair riser as between 6 and 7¾ in. Local codes vary, so check with your building department.
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Sources
Formulas and reference values are from these sources. Page content last updated 2026-10-19.