Deck Stair Calculator
Get your step count, riser height, stringer length, lumber list, and cost estimate — all per IRC R311.7 building code.
Last updated: March 7, 2026
Enter Stair Details
inches
Measure from deck surface to ground level
in
Min 10" per IRC code
in
Min 36" per IRC code
Stringer sits against the deck frame
3 for 36" width
Results
IRC Code: Compliant
Rise: ✓ 6.86" (max 7¾")
Run: ✓ 11" (min 10")
Width: ✓ 36" (min 36")
Comfort (2R+T): 24.71" — Ideal (24-25")
Steps
6
Riser Height
6.86"
Total Run
66" (5.5 ft)
Stringer Length
77.77" (6.48 ft)
Stair Angle
31.94°
Railing
Required
Materials List
Stringers (2×12): 3 × 8 ft
Treads (5/4×6): 12 × 3 ft
Posts (4×4): 3 × 4 ft
Hardware sets: 3
Railing: 6.48 lin ft
Cost Estimate
Stringers:$36
Treads:$72
Posts:$18
Railing:$97.2
Hardware:$36
Materials subtotal:$259.2
Labor (pro install):$210
Total:$469.2
Shopping Tips
- • Buy 2×12 stringers at least 1 ft longer than calculated (6.48 ft) for top/bottom cuts
- • 12 tread boards (5/4×6) — buy 1-2 extra for mistakes
- • Railing required (deck over 30" high) — check local code for post spacing
- • Stringer brackets ($8-15 each) attach stringers to the deck frame
- • Use exterior-rated screws (deck screws, not drywall screws)
How to Use This Calculator
1. Measure
Measure from deck surface straight down to the ground (total rise)
2. Enter
Enter deck height, tread depth, width, and select your tread type
3. Review
Check IRC compliance, comfort rating, and review the materials list
4. Order
Copy the materials list and head to your local lumber yard
How We Calculate
Number of Risers = ⌈Total Rise ÷ 7.5"⌉
Actual Riser Height = Total Rise ÷ Number of Risers
Stringer Length = √(Stringer Height² + Total Run²)
IRC R311.7 Requirements
- • Maximum Rise: 7¾" per step
- • Minimum Run: 10" per step
- • Minimum Width: 36" (residential)
- • Rise Variation: ≤ 3/8" between steps
- • Handrail: required if ≥ 4 risers
Comfort Formula
- • 2R + T = 24-25" (ideal range)
- • R = Riser Height, T = Tread Depth
- • Example: 7" rise + 11" tread = 25" ✓
- • Stringers: always cut from 2×12
- • Stringer spacing: 16-24" on center
Stair dimensions per IRC 2021 R311.7 standards and American Wood Council (AWC) design guidelines.