Stairs for a 120 inch rise: steps, riser height and stringer length
A 120 inch (10 ft 0 in) total rise needs 16 risers of 7 1/2" and 15 treads under the 2021 IRC. Run, stringer length and lumber size for 10 to 11 inch treads.
Open this rise in the calculator for your exact tread size, tread thickness and a printable cut sheet.
Residential stairs (2021 IRC: riser up to 7 3/4", tread at least 10")
| Tread run | Risers | Riser height | Treads | Total run | Stringer cut line | 2x12 to buy | Code |
|---|---|---|---|---|---|---|---|
| 10" | 16 | 7 1/2" | 15 | 12' 6" | 16' 1/16" | 18 ft | pass |
| 10 1/2" | 16 | 7 1/2" | 15 | 13' 1 1/2" | 16' 6" | 18 ft | pass |
| 11" | 16 | 7 1/2" | 15 | 13' 9" | 17' 0" | 20 ft | pass |
Commercial stairs (2021 IBC: riser 4" to 7", tread at least 11")
| Tread run | Risers | Riser height | Treads | Total run | Stringer cut line | 2x12 to buy | Code |
|---|---|---|---|---|---|---|---|
| 10" | 18 | 6 11/16" | 17 | 14' 2" | 17' 4 1/16" | 20 ft | check |
| 10 1/2" | 18 | 6 11/16" | 17 | 14' 10 1/2" | 17' 11 1/16" | 20 ft | check |
| 11" | 18 | 6 11/16" | 17 | 15' 7" | 18' 6 3/16" | 20 ft | pass |
| 11 1/2" | 18 | 6 11/16" | 17 | 16' 3 1/2" | 19' 1 3/8" | over 20 ft | pass |
How this is worked out
120 inches divided by the maximum riser, rounded up, gives the number of risers. Each riser is 120 inches divided by that number. With the upper floor as the top step there is one tread fewer than risers. The 2x12 size allows one extra step diagonal for the top and bottom cuts. Treads are assumed 1 inch thick, so the bottom riser on the stringer is cut 1 inch shorter.
Measure your own total rise from finished surface to finished surface. Your local building department may use a different code edition or amendments.