The Stair Calculator works out the number of steps, riser height, tread depth, angle and stringer length for a straight staircase.
19 steps with 6.32 in risers
| Number of risers (steps) | 19 |
| Riser height | 6.32 in |
| Number of treads | 18 |
| Tread depth | 10.00 in |
| Angle | 32.3° |
| Stringer length | 18.73 ft |
| Building code check (IRC: rise ≤ 7.75 in, tread ≥ 10 in) | Passes |
| 2R + T comfort rule (24–25 in ideal) | 22.63 in |
Total rise is the vertical height from floor to floor. Total run is the horizontal length the stairs cover. Each step has a riser (vertical) and a tread (horizontal). Stringers are the sloped boards that support the treads.
The calculator divides the total run by the tread depth to get the number of treads; there is one more riser than treads. Riser height = total rise ÷ number of risers. Angle = arctan(riser ÷ tread).
Worked example (defaults): 10-inch treads, 15 ft total run and 10 ft total rise give 18 treads, 19 risers of 6.32 in and an angle of about 32°.
The U.S. International Residential Code allows a maximum riser of 7¾ in and a minimum tread of 10 in, with no more than ⅜ in variation between steps. Headroom must be at least 6 ft 8 in. Comfortable stairs follow 2 × riser + tread ≈ 24–25 in.
What is a good stair angle? 30–37°.
Do I count the top floor as a tread? No, the upper floor acts as the last step.
Always check local codes before building.