Stair Calculator
Riser height and tread depth for a straight flight.
How it works
For a straight flight terminating at the upper floor, the number of treads is one less than the number of risers. Rise is total height divided by risers; tread depth is the horizontal run divided by treads. This calculates geometry from your chosen count.
Related calculators
How the Stair Calculator works
Calculate the geometry of a straight stair flight from finished floor-to-floor height, total horizontal tread run and a chosen number of risers. The upper floor supplies the final walking surface.
Risers and treads are different counts
At 9 ft total height and 16 risers, rise is 108/16 = 6.75 in. There are 15 treads; a 12 ft horizontal tread run gives 144/15 = 9.6 in per tread. These numbers illustrate the calculation and are not a recommended stair design.
Pitch is arctan(rise/going), about 35.1° in this example. Going excludes nosing projection. The run used here describes the sum of tread depths, so measure it consistently rather than substituting an opening dimension.
Measure finished surfaces
Use the future finished floor levels at both ends of the flight. Flooring thickness can otherwise change the first or last riser. A landing or a separate upper tread changes the counting convention and needs its own layout.
Total tread area is tread count × tread depth × flight width. It can help estimate tile or lumber for the walking surfaces, but does not include riser faces, nosings, supporting stringers or fastening.
FAQ
Why is there one fewer tread? expand_more
The upper floor acts as the final walking surface in this straight-flight convention.
Does this check building-code compliance? expand_more
No. Check the selected geometry against the requirements for the actual installation and project.
Can I use it for winding stairs? expand_more
No. Winders, landings and curved stairs need a different geometric layout.