Stair & stringer calculator (IRC)
Enter your total height (finished floor to finished floor, or ground to deck) and this lays out a code-compliant stair: number of risers, exact riser height, number of treads, total run, and stringer length. Riser and tread limits come from the International Residential Code.
5 risers
Risers (steps)
- Riser height (each)
- 7.20 in
- Treads
- 4 treads
- Total run (horizontal)
- 44.0 in
- Stringer length (min)
- 56.9 in
What this assumes
- Risers = ceil(36 in ÷ 7.75 in max) = 5; each riser = 7.20 in.
- Treads = risers − 1 = 4; total run = 4 × 11 in = 44.0 in.
- Stringer ≈ √(rise² + run²) = 56.9 in (board length before cuts).
Coverage rates & sources
Every number this calculator uses is a published engineering constant — not an estimate we made up. Here is exactly what it assumes and where each value comes from.
- Max riser height: 7¾ in (7.75 in)Source: International Residential Code (IRC) R311.7.5.1 — residential stair risers
- Min tread depth: 10 inSource: International Residential Code (IRC) R311.7.5.2 — residential stair treads
- Max riser variation: ⅜ in within a flightSource: International Residential Code (IRC) R311.7.5.1 — uniformity of risers
Before you buy
- Spreading the rise over an equal number of risers keeps each one ≤ 7¾ in (IRC); the greatest and smallest riser in a flight may differ by no more than ⅜ in.
- Your local jurisdiction may amend the IRC — always confirm riser, tread, handrail, and landing requirements with your building department before cutting stringers.
- Stringer length is the straight diagonal; add length for the top/bottom cuts and any landing or overhang.
This is a planning estimate, not a substitute for a pro's on-site measurement. For load-bearing, structural, or code-regulated work, confirm quantities with a licensed contractor.
Frequently asked
How many steps do I need for a 3-foot-high deck?
For 36 inches of rise, 36 ÷ 7.75 rounds up to 5 risers at about 7.2 inches each, with 4 treads. At an 11-inch tread that's a 44-inch total run. Always verify against your local code.
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