Calculate rise, run, and number of steps for your deck stairs. IRC code-compliant.
How to Use This Deck Stair Calculator
Measure the total rise — the vertical distance from the ground to the top of your deck surface. Enter your maximum riser height (7-3/4" is the IRC maximum; 7" is more comfortable). Choose your desired tread depth. The calculator determines the number of risers and treads, exact riser height, and total horizontal distance the stairs will extend from the deck.
The formula is: Number of Risers = Total Rise ÷ Max Riser Height (rounded up). Exact riser height = Total Rise ÷ Number of Risers. Treads = Risers - 1. Total run = Treads × Tread Depth.
How to Build Code-Compliant Deck Stairs
Deck stairs are one of the most regulated parts of residential construction — and for good reason. A poorly built set of stairs is a safety hazard for your family and a liability risk. This guide covers the IRC requirements and practical tips.
Key IRC Requirements (2024)
- Maximum riser height: 7-3/4 inches. All risers within a flight must not vary by more than 3/8 inch between the tallest and shortest.
- Minimum tread depth: 10 inches (measured nose-to-nose). If you omit stair nosings, you must provide a full 11-inch tread.
- Minimum stair width: 36 inches clear width. If your deck is wider than 36 inches, match the stair width to the door or landing.
- Handrails: Required on at least one side for stairs with 4 or more risers. Must be 34-38 inches high measured from the stair nosing.
- Landing: A level landing at least 36 inches deep is required at the bottom of the stairs. The landing must be the same width as the stairs.
Comfort Rule
Carpenters use the comfort formula: 2 × Riser Height + Tread Depth = 24 to 25 inches. A 7-inch riser with an 11-inch tread gives 2(7) + 11 = 25 — right in the sweet spot. A 7.75-inch riser with a 10-inch tread gives 25.5, which is steeper but still code-compliant.
How to Cut Stringers
Use pressure-treated 2×12 lumber for stringers. Mark each rise and run with a framing square and stair gauges. Cut precisely with a circular saw, finishing the corner with a handsaw — never overcut with a circular saw as this weakens the stringer. Stringers should be spaced no more than 16 inches on center for stability.