Calculate stair dimensions including number of steps, riser height, tread depth, total run, and stringer length. Meets IRC residential building code guidelines for safe, comfortable stairs.
Estimates only — always verify stair dimensions against your local building code before construction.
Building stairs for a 9-foot (108-inch) floor-to-floor rise with a 7.5-inch target riser? You need 15 risers at 7.20 inches each, with 14 treads at 10 inches. The total run is 140 inches (11.7 feet) and the stringer length is about 14.7 feet. This meets IRC residential code requirements.
Based on 10-inch tread depth
| Total Rise | Steps | Riser Height | Total Run | Stringer |
|---|---|---|---|---|
| 3 ft (36 in) — deck | 5 | 7.20 in | 3.3 ft | 4.5 ft |
| 6 ft (72 in) | 10 | 7.20 in | 7.5 ft | 9.6 ft |
| 8 ft (96 in) | 13 | 7.38 in | 10.0 ft | 12.8 ft |
| 9 ft (108 in) | 15 | 7.20 in | 11.7 ft | 14.7 ft |
| 10 ft (120 in) | 16 | 7.50 in | 12.5 ft | 16.0 ft |
With standard framing, floor-to-floor height is about 105–110 inches. At a comfortable 7.5-inch rise, that's 14–15 steps.
7.75 inches for residential stairs (IRC). 7 inches for commercial stairs (IBC). Most comfortable range is 7–7.5 inches.
10 inches for residential (IRC), 11 inches for commercial (IBC). Tread depth is measured from nosing to nosing, not including the overhang.
Use the Pythagorean theorem: stringer = √(total rise² + total run²). For a 9-foot rise with 11.7 feet of run, the stringer is about 14.7 feet.
Between 30 and 35 degrees. Steeper stairs feel unsafe, shallower stairs waste floor space. A 7-inch rise with an 11-inch run gives about 32 degrees.
The most widely used comfort formula is from architect Francis Ching: two risers plus one tread should equal 24 to 25 inches (2R + T = 24–25). The ideal stair angle is between 30 and 35 degrees. A classic 7-inch rise with an 11-inch tread scores 25 on the Ching formula and hits 32.5 degrees — considered the gold standard for residential stairs.
Typical Results
💡 Total rise should be ~105–110" for standard 8' ceiling. If riser count seems off, recheck measurement.