15-Step Stair Stringer: Dimensions, Length & Cut Angle
Fifteen steps serves 9-foot ceilings with deep floor framing, pushing past 112 inches of rise. Every row is computed by the same engine as our interactive calculator.
15-step stringer dimensions · 10.5" tread
| Total Rise | Rise per Step | Total Run | Stringer Length | Cut Angle |
|---|---|---|---|---|
| 109" (9' 1") | 7.27" (7 1/4") | 147" | 183.0" (183") | 34.7° |
| 110" (9' 2") | 7.33" (7 5/16") | 147" | 183.6" (183 5/8") | 34.9° |
| 111" (9' 3") | 7.40" (7 3/8") | 147" | 184.2" (184 3/16") | 35.2° |
| 112" (9' 4") | 7.47" (7 7/16") | 147" | 184.8" (184 13/16") | 35.4° |
| 113" (9' 5") | 7.53" (7 1/2") | 147" | 185.4" (185 7/16") | 35.7° |
| 114" (9' 6") | 7.60" (7 9/16") | 147" | 186.0" (186") | 35.9° |
| 115" (9' 7") | 7.67" (7 5/8") | 147" | 186.6" (186 5/8") | 36.1° |
| 116" (9' 8") | 7.73" (7 11/16") | 147" | 187.3" (187 1/4") | 36.4° |
Total run is fixed at 147" for 15 steps with a 10.5" tread: (steps − 1) × tread, because the upper floor or deck acts as the top step. For a different tread depth, total run = 14 × tread.
Rise per step is floored to the nearest 1/16" for framing-square layout. Different total rise? Use the interactive stringer calculator.
When do you need 15 steps?
Fifteen steps serves 9-foot ceilings with deep floor framing, pushing past 112 inches of rise.
A 15-step stringer covers total rises from 109" (9' 1") to 116" (9' 8") while keeping every riser at or under the IRC maximum of 7¾" (R311.7.5.1). Below 109", use a 14-step stringer; above 116", move to 16 steps.
What board do you need?
The longest stringer in the table is 187.3", so a 16-foot 2×12 covers every case with layout margin. Use solid, straight-grained 2×12 stock — after notching, the remaining "throat" must keep at least 3.5" of material for structural integrity.
Code checkpoints for a 15-step stair
- Handrail required. 15 risers is at or over the 4-riser threshold — a graspable handrail is required on at least one side (IRC R311.7.8).
- Guards required. Every total rise in the 15-step range exceeds 30", so open sides of the walking surface need 36" guards (IRC R312.1.1–.2) — see the baluster spacing calculator.
- Riser uniformity: the largest and smallest riser may differ by no more than 3/8" (IRC R311.7.5.1) — divide total rise by 15 and mark every notch from the same reference edge.
- Drop the bottom riser by one tread thickness so the first step matches the rest after treads go on.