Stair calculator — risers, treads and pitch
Stairs are set out from the floor-to-floor height, not from a chosen riser. Divide the rise by the number of risers you want and check the result against code: risers must be equal, and the 2R+G rule tells you whether the flight will actually feel comfortable.
stair calculator
- Riser height
- 187.5mm
- Total going
- 4,200 mm over 15 treads
- Pitch
- 33.8°
- 2R + G
- 655 mm — within comfort range
Formula
riser = rise ÷ number of risers · treads = risers − 1 · pitch = atan(riser ÷ going)Comfort rule of thumb: 2 × riser + going should land between 550 and 700 mm. Typical private stairs use 150–190 mm risers with a 250–300 mm going and a pitch at or below 42°.
Worked examples
| Input | Result |
|---|---|
| 3000 mm rise, 16 risers | 187.5 mm risers, 15 treads, 33.8° pitch |
| 3000 mm rise, 18 risers | 166.7 mm risers — more comfortable, 560 mm longer |
| 2700 mm rise, 15 risers | 180 mm risers, 14 treads |
Questions
Why is the tread count one less than the riser count?
The top riser lands on the upper floor slab, which acts as the final tread. A flight with 16 risers has 15 treads, so total going is 15 × going.
What riser height should I use?
150–190 mm covers most residential codes; public and escape stairs are usually capped nearer 170 mm. Risers must all be equal within a few millimetres — unequal risers are the classic trip hazard flagged on site.
How do I model this in Revit?
Set the stair type's maximum riser height and minimum tread depth first, then let Revit derive the riser count from the level-to-level height. Typing a riser count over a mismatched level height is what produces the unequal-riser warning.