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: June 21, 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.
Frequently Asked Questions
Take your deck height in inches and divide by 7.5 — that gives you the number of risers. A 48-inch deck works out to 7 risers and 6 treads, since the deck surface counts as the top step. IRC R311.7 caps each riser at 7¾", and the calculator adjusts automatically to stay within code.
Always use 2×12 boards for stringers. The board needs to cover the full diagonal from the bottom pad to the last tread — for a 48" deck with 11" treads, that's about 6.5 feet. Grab boards at least 1 foot longer than the calculated length so you have room for the top and bottom cuts.
Per IRC code, any stairway with 4+ risers needs a handrail, and you need guards (36" min height) once the total rise goes past 30 inches. Most decks are well above 30", so yeah, you'll almost always need railing. Posts usually go every 6 feet along the stringer.
For stairs up to 36" wide, go with 3 stringers — one on each side plus one in the center. Add another stringer for every extra 16-24 inches of width. A 48" wide staircase? That's 4 stringers. The center ones keep the treads from bouncing when people walk on them.
For a basic 4-foot deck with 6 treads, expect $300-$600 in materials (stringers, treads, hardware). Railing adds another $200-$400. Hiring a pro? That's $250-$500 for labor depending on the setup. All in, most homeowners spend $500-$1,200 for a standard set of deck stairs.
A landing splits the staircase into two separate runs. Measure the height from the deck to the landing, then from the landing to the ground — run the calculator twice, once for each section. IRC requires landings to be at least 36 inches deep and as wide as the stairs. Most people add a landing when total rise exceeds 12 feet or when the stairs need to change direction.
IRC R311.7 covers the big ones: max riser height is 7¾", min tread depth is 10", and the variation between any two risers can't exceed ⅜". You also need a graspable handrail (34-38" high) on stairs with 4+ risers, and guards at least 36" tall on open sides. Local codes sometimes add stricter rules, so always check with your building department before you start cutting.
Aim for a riser height near 7" and a tread depth of 10-11" — comfortable for most people and well within IRC limits (max 7¾" riser, min 10" tread). A quick comfort check: 2 × riser + tread should land around 25". Keep every riser within ⅜" of the others so the stairs feel even underfoot.
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