Stair Stringer Calculator – Cut Stairs Right | CalcLoft
Calculate risers, treads and stringer length for your stairs.
Stair math, simplified
- Risers: total rise ÷ target riser (7 in), rounded up
- Actual riser: total rise ÷ number of risers (must be ≤ 7.75)
- Treads: risers − 1
- Stringer length: √(total run² + total rise²) where run = treads × tread depth
Example: 105 in rise ÷ 7 = 15 risers → 14 treads → run 154 in → stringer √(154² + 105²) ≈ 186 in (15.5 ft).
Code reminders (US typical)
- Riser height: 4-7.75 inches max
- Tread depth: min 10 inches
- Stringer spacing: every 16-18 inches across the width
- Always verify with your local building code
Stair calculator FAQ
How many steps for a 9 ft ceiling?
About 105-110 in total rise ÷ 7 in = 15 steps.
What is the max riser height?
Typically 7.75 inches (IRC). Keep it under that to pass inspection.
How many stringers for a 4 ft wide stair?
3 stringers — one on each side and one in the middle.
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