Deck Stairs Calculator
Enter the height from the ground to your deck surface and get a code-friendly stair layout: risers, riser height, treads, total run, and stringer length.
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How to calculate deck stairs
Divide your total rise by a target riser height (around 7–7.5") and round to a whole number of risers, then divide the rise by that count for the exact riser height. Treads always equal risers minus one. Multiply treads by tread depth for total run, and use the Pythagorean theorem (rise² + run²) for stringer length.
Deck stair code basics
Under the IRC, risers may be no taller than 7¾" and treads no shorter than 10", and every riser must be within 3/8" of the others. Stringers are typically spaced 16" on center. Always confirm with your local building department.
Frequently asked questions
- How many stringers do I need?
- One every 16" of width plus one — so a 48" stair uses four stringers. Wider treads or composite need closer spacing.
- Why did my riser height change?
- Risers must be equal, so the calculator rounds to whole risers and recomputes the exact height to match your total rise.
Next steps
- Deck Cost Calculator — total project price.
- Deck Board Calculator — boards and screws.
- Footing & Concrete Calculator — posts and concrete.