What it works out
Enter the height from floor to floor. Add the run if the stairs must fit a set length, and the headroom and floor thickness if you want the stairwell opening. You get the number of risers, the riser height, the number of treads, the tread width, the stringer length and the angle of incline. It starts from the target riser height and tread width stored in Settings and shows how far the rounded result is over or under them. It is a layout aid, not a code check.
The formula
- Risers
- rise ÷ desired riser, rounded
- Riser
- rise ÷ risers
- Treads
- risers − 1
In words: Risers = rise divided by desired riser, rounded; riser = rise divided by risers; treads = risers minus 1
Worked example
A floor-to-floor height of 108 in with a 7.5 in target riser
- Total rise 108 in
- Target riser 7.5 in
- Risers = 108 ÷ 7.5 = 14.4, rounded to 14
- Riser height = 108 ÷ 14 = 7.714 in
- Treads = 14 − 1 = 13
With a 10 in tread, the run is 13 × 10 = 130 in. The app also shows the stringer length and the angle.
Good to know
- A layout aid, not a code check: confirm riser, tread and headroom limits with your local authority.
- Targets come from your settings and can be changed per project.
- A calculator, not a building-code check: confirm local rules with your building authority.
Questions
Does this check building code?
No. It lays out equal risers and treads from your targets. Always check your local rules.
Why is there one less tread than risers?
The top riser lands on the upper floor, which acts as the last tread.