Deck Stair Calculator
Calculate deck stair dimensions including riser height, tread depth, and step count for safe stairs.
Formula & Explanation
The deck stair calculator computes safe stair dimensions using the "7-11 Rule" from the IRC (International Residential Code). Step Count: Round up Total Rise ÷ 7.5 inches Adjusted Riser: Total Rise ÷ Step Count Tread Depth: 17 inches - Adjusted Riser Height (minimum 10") The 7-11 rule states that rise + run should equal 17-18 inches for comfortable stairs. A riser of 7-8 inches with a tread of 10-11 inches is typical. Number of Treads = Number of Steps - 1 (the top step is the deck itself)
Assumptions
- •Total rise is measured from ground level (grade) to the deck surface
- •The 7.5-inch standard riser height is used as the baseline for calculations
- •Riser height should be within 7-8 inches per building code (3/8" tolerance between steps)
- •Tread depth minimum is 10 inches (from riser to edge)
- •Number of treads is one less than number of risers (the deck is the final step)
- •Stairs follow the 7-11 rule: rise + run = 17-18 inches for safe, comfortable stairs
- •All steps must have uniform dimensions - no variable step heights allowed
Example Calculation
A 36-inch rise deck requires 5 steps with 7.2-inch risers and 9.8-inch treads, following safe stair proportions.
Inputs
Results
Typical Deck Stair Dimensions and Building Code Compliance
| rise | steps | riser | tread | rule |
|---|---|---|---|---|
| 24" | 4 | 6" | 11" | Complies |
| 30" | 4 | 7.5" | 9.5" | Complies |
| 36" | 5 | 7.2" | 9.8" | Complies |
| 42" | 6 | 7" | 10" | Complies |
| 48" | 7 | 6.9" | 10.1" | Complies |
| 54" | 8 | 6.75" | 10.25" | Complies |
| 60" | 9 | 6.67" | 10.33" | Complies |
| 72" | 10 | 7.2" | 9.8" | Complies |
Frequently Asked Questions
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