Deck Stair Calculator
Enter your deck height to get the riser count, tread count, stringer length and a 2×12 lumber list — a 4 ft rise works out to 7 risers and 6 treads. You also get a cost estimate and IRC R311.7 checks.
Last updated: September 30, 2026
Enter Stair Details
inches
Measure from deck surface to ground level
in
Min 10" per IRC code
in
Min 36" per IRC code
Results
Steps
6
Riser Height
6.86"
Stringer Length
77.77" (6.48 ft)
IRC R311.7: Compliant Comfort: Ideal
Total Run
66" (5.5 ft)
Stair Angle
31.94°
Cost Estimate
Stringers:$36
Treads:$72
Posts:$18
Railing:$97.2
Hardware:$36
Materials subtotal:$259.2
Labor (pro install):$210
Total:$469.2
Rates: framing $1.5/lin ft · deck board $2/lin ft — edit in Advanced settings
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
IRC Code: Compliant
Rise: ✓ 6.86" (max 7¾")
Run: ✓ 11" (min 10")
Width: ✓ 36" (min 36")
Comfort (2R+T): 24.71" — Ideal (24-25")
Shopping Tips
- • Railing required (deck over 30" high) — check local code for post spacing
- • Stringer brackets ($8-15 each) attach stringers to the deck frame
Stair Layout Diagram
Deck Height Reference
Risers and treads for common deck heights, at the default 11 in tread depth.
| Deck height | Risers | Treads | Riser height | Total run |
|---|---|---|---|---|
| 2 ft (24") | 4 | 3 | 6 in | 2.75 ft |
| 3 ft (36") | 5 | 4 | 7.2 in | 3.67 ft |
| 4 ft (48") | 7 | 6 | 6.86 in | 5.5 ft |
| 5 ft (60") | 8 | 7 | 7.5 in | 6.42 ft |
| 6 ft (72") | 10 | 9 | 7.2 in | 8.25 ft |
| 8 ft (96") | 13 | 12 | 7.38 in | 11 ft |
Worked Examples
4 ft Deck
48" rise · 11" tread · 36" wide
7 risers · 6 treads · 6.86" riser · 66" run · 6.48 ft stringer · 8 ft 2×12 board
3 ft Deck
36" rise · 10" tread · 36" wide
5 risers · 4 treads · 7.2" riser · 40" run · 4.11 ft stringer · 6 ft 2×12 board
6 ft Deck
72" rise · 11" tread · 48" wide
10 risers · 9 treads · 7.2" riser · 99" run · 9.86 ft stringer · 11 ft 2×12 board
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
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.
Stringers are always 2×12 boards. The board has to span the full diagonal from the bottom pad to the last tread — for a 48" deck with 11" treads that's about 6.5 feet, and the calculator prints the exact length. Buy boards at least 1 foot longer than the calculated length so you have room for the top and bottom cuts.
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.
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