Complete guide
Stair calculator for risers, treads, run and stringer length
Enter total rise, a target maximum riser, tread depth and stair width. Calculator24 chooses a whole riser count and returns the actual rise, typical tread count, total run, pitch and straight stringer length.
Measure the total rise
Total rise is the finished vertical distance from the lower walking surface to the upper finished floor. Include planned flooring thickness before final layout.
Stair geometry formulas
A staircase needs a whole number of equal risers, so the preliminary division is rounded upward. A common straight flight has one fewer tread than risers because the upper floor acts as the final walking surface.
risers=ceiling(total rise÷target riser)actual riser=total rise÷riserstreads=risers−1stringer=√(rise²+run²)Worked 108-inch example
Dividing 108 inches by a 7.5-inch target gives 14.4, which rounds up to 15 risers. Every equal riser is then 7.2 inches, and 14 ten-inch treads produce 140 inches of run.
2021 IRC reference values
The cited 2021 International Residential Code sections use a maximum 7.75-inch riser and a minimum 10-inch tread for the covered residential stairs, with measurement and variation rules in the same provisions.
Codes and site conditions vary
Local jurisdictions can adopt another edition or amendments. Stair type, occupancy, winders, spiral stairs, landings, headroom, handrails and guards require checks beyond this geometry.
Before cutting stringers
Confirm finished dimensions on site, account for tread and landing materials, verify support and fastening details, and have the complete layout reviewed where required.
Geometry outputs
| Output | Meaning |
|---|---|
| Riser count | Number of equal vertical steps |
| Actual riser | Total rise divided by whole risers |
| Tread count | Usually one fewer than risers |
| Total run | Tread count multiplied by tread depth |
| Stringer length | Straight diagonal from rise and run |
Frequently asked questions
Why round the riser count up?
It keeps the equal actual riser at or below the target height.
Why is there one fewer tread?
In a typical straight flight, the upper floor serves as the final walking surface.
Does this prove code compliance?
No. It provides geometry and a cited reference; local requirements control.
Are flooring thicknesses included?
Only if the total rise and dimensions you enter include finished surfaces.
What is stringer length?
It is the straight diagonal calculated from total rise and run.
Can I use centimeters?
Yes. All geometric outputs remain in the selected unit.
What to keep in mind
This is geometric planning only. Building-code editions, occupancy, landings, headroom, nosing, handrails, guards and local amendments must be verified with the authority having jurisdiction and a qualified professional.
Results display up to 8 decimal places; exported numbers preserve calculation precision. This is a calculation summary, not an official certificate.