Stair Calculator
From total rise to riser count, tread run, and approximate stringer length. Click any i for detail.
Stair geometry
Total rise (in)
i
Total rise
Finished floor to finished floor, in inches. |
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|---|---|
Target riser (in)
i
Target riser
Comfortable residential target is often ~7 in (codes cap near 7¾ in). |
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Tread depth (in)
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Tread depth
Horizontal going, nosing excluded. Codes often want ≥10 in residential. |
How to use this calculator
- Measure total rise in inches.
- Pick a target riser height.
- Enter tread depth.
- Read riser count, actual riser, run, and stringer length.
Results explained
Risers are rounded so height stays even. Treads = risers − 1 on a simple straight run. Stringer ≈ √(rise² + run²).
Quick reference: stairs
Common residential targets (verify local code).
| Item | Detail |
|---|---|
| Max riser (many IRC) | 7¾ in |
| Min tread (many IRC) | 10 in |
| 2R + T rule of thumb | ≈ 24–25 in |
| Headroom | Often 6′8″ min |
Open risers, winders, and landings need a different layout.
How the estimate is built
risers ≈ round(total rise ÷ target). actual riser = total rise ÷ risers. run = (risers − 1) × tread. stringer ≈ √(rise² + run²).
Example scenario
105 in total rise with a 7 in target → 15 risers at 7.00 in, 14 treads × 10 in = 140 in run.
FAQ
Why not 7.5 exactly?
Rise must divide evenly so every riser matches. Uneven risers are a trip hazard.
Is the stringer the board length?
It’s the hypotenuse sketch. Add extra for top/bottom seats before you cut.
Can I use this for deck stairs?
Same geometry. Footings, stringer count, and guards are separate.