13-Step Stair Stringer: Dimensions, Length & Cut Angle
Thirteen steps is one of the two most common interior flight sizes for 8-foot ceilings with standard floor framing. Every row is computed by the same engine as our interactive calculator.
13-step stringer dimensions · 10.5" tread
| Total Rise | Rise per Step | Total Run | Stringer Length | Cut Angle |
|---|---|---|---|---|
| 94" (7' 10") | 7.23" (7 3/16") | 126" | 157.2" (157 3/16") | 34.6° |
| 95" (7' 11") | 7.31" (7 1/4") | 126" | 157.8" (157 13/16") | 34.8° |
| 96" (8') | 7.38" (7 3/8") | 126" | 158.4" (158 3/8") | 35.1° |
| 97" (8' 1") | 7.46" (7 7/16") | 126" | 159.0" (159") | 35.4° |
| 98" (8' 2") | 7.54" (7 1/2") | 126" | 159.6" (159 5/8") | 35.7° |
| 99" (8' 3") | 7.62" (7 9/16") | 126" | 160.2" (160 1/4") | 36.0° |
| 100" (8' 4") | 7.69" (7 11/16") | 126" | 160.9" (160 7/8") | 36.2° |
Total run is fixed at 126" for 13 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 = 12 × 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 13 steps?
Thirteen steps is one of the two most common interior flight sizes for 8-foot ceilings with standard floor framing.
A 13-step stringer covers total rises from 94" (7' 10") to 100" (8' 4") while keeping every riser at or under the IRC maximum of 7¾" (R311.7.5.1). Below 94", use a 12-step stringer; above 100", move to 14 steps.
What board do you need?
The longest stringer in the table is 160.9", so a 14-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 13-step stair
- Handrail required. 13 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 13-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 13 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.