Stair stringers for a 3 ft (36 in) high deck
A 3 ft (36 in) high deck needs 5 risers of 7-3/16 inches each and 4 treads — the deck surface is the top step. With 10½ inch treads the stairs reach 42 inches (3 ft 6 in) out from the deck, and each stringer measures about 55-5/16 inches (4 ft 7-5/16 in) along the slope.
How to work it out
- 36 in ÷ 7.75 in max = 4.65 → round up to 5 risers, each 36 in ÷ 5 = 7-3/16 in strong (7.2 in)
- 4 treads × 10-1/2 in = 42 in run · √(36² + 42²) = 55-5/16 in along the slope
- Comfort check: 2 × 7-3/16 in + 10-1/2 in = 24.9 in (24–26 in is comfortable) · stair angle 34.4 degrees
- Throat: 11-1/4 in board − 5.94 in notch depth = 5-5/16 in
- Tread board: 10-1/2 in tread + 3/4 in nosing + 0 in riser board = 11-1/4 in
- Top level cut: 7-3/16 in riser + 1 in tread = 8-3/16 in below the deck surface
Two 5/4×6 deck boards (5½ in each) plus a ¼ in gap are 11¼ in deep. Cutting the notch 10½ in lets the front board overhang the step below by about ¾ in (the nosing). Measure the rise from the deck surface to the pad or ground where the bottom step will actually sit.
Adjust for your project
More options: Max riser · Spacing · Stringer board …
- Steps to cut
- 4 steps to cut in each stringer + the deck is the top step
- Total run (how far the stairs reach out)
- 42 in (3 ft 6 in)
- Stringer length (along the slope)
- 55-5/16 in (4 ft 7-5/16 in)
- Stringers needed
- 4 stringers
- Stringer stock to buy
- 4 × 2×12 × 8 ft
- Tread board depth to buy (tread + nosing + riser board)
- 11-1/4 in
- Drop the stringer (trim off the bottom)
- 1 in
- Top level cut, measured down from the top surface
- 8-3/16 in
- Wood left below the notches (throat)
- 5-5/16 in
| Item | What to buy | Notes |
|---|---|---|
| Stringers | 4 × 2×12 × 8 ft | Pressure-treated and rated for ground contact (check the end tag) — the bottoms sit near the ground. |
| Treads | 8 pieces 36 in long (2 per step) → buy 3 × 5/4×6 × 10 ft | 2 boards 5½ in wide with ¼ in gaps cover 11-1/4 in of the 11-1/4 in each step needs; 3 pieces per 10 ft board. |
| Hardware | Sloped joist hangers or a hanger board at the top (DCA 6 Fig. 31); screws or nails rated for treated lumber (hot-dip galvanized or stainless) | Plus a handrail on at least one side — four or more risers (2021 IRC R311.7.8). |
Where to mark each step (height above the bottom)
| Step | Height above the bottom | Guard on open sides? |
|---|---|---|
| Tread 1 | 7-3/16 in | — |
| Tread 2 | 14-3/8 in | — |
| Tread 3 | 21-5/8 in | — |
| Tread 4 | 28-13/16 in | — |
| Deck surface | 36 in | Yes — over 30 in |
One step fewer or more
| Risers | Each step | Treads | Tread depth | Total run | Check |
|---|---|---|---|---|---|
| 4 risers | 9 in | 3 | 10-1/2 in | 31-1/2 in | Risers too tall |
| 5 risers (shown) | 7-3/16 in | 4 | 10-1/2 in | 42 in | OK |
| 6 risers | 6 in | 5 | 10-1/2 in | 52-1/2 in | OK |
- Each step is marked to the nearest 1/16 in. Stepping off 7-3/16 in 5 times would put the top 1/16 in low, so mark each step from the Where to mark each step table below instead.
- The 4 stringers come from the 16 in default spacing — the joist spacing 5/4 wood decking needs on a deck (2021 IRC Table R507.7). DCA 6 allows cut stringers up to 18 in apart — 3 for this width — if your tread boards are rated for that span (check the tread maker).
- What the bottom sits on: DCA 6 doesn’t let deck stringers bear on a pad or patio that isn’t founded below frost depth — set them on posts or footings. See what the bottom of the stringers sits on.
- Leave a landing at the bottom at least 36 in deep and as wide as the stair (IRC R311.7.6); the deck is the top landing.
- Trim 1 in off the bottom of each stringer (one tread thickness) so the first step comes out the same 7-3/16 in as the rest.
Run and stringer length for a 36 in rise, by tread depth
| Tread depth | Total run (how far the stairs reach out) | Stringer length (along the slope) | Tread board depth to buy (tread + nosing + riser board) |
|---|---|---|---|
| 10 in | 40 in (3 ft 4 in) | 53-13/16 in (4 ft 5-13/16 in) | 10-3/4 in |
| 10.5 in | 42 in (3 ft 6 in) | 55-5/16 in (4 ft 7-5/16 in) | 11-1/4 in |
| 11 in | 44 in (3 ft 8 in) | 56-7/8 in (4 ft 8-7/8 in) | 11-3/4 in |
| 11.25 in | 45 in (3 ft 9 in) | 57-5/8 in (4 ft 9-5/8 in) | 12 in |
| 12 in | 48 in (4 ft) | 60 in (5 ft) | 12-3/4 in |
What to know about stairs for a 3 ft deck
Five risers puts this flight past the handrail trigger: IRC R311.7.8 wants a handrail on at least one side of any flight with four or more risers, 34–38 in above the nosings. The deck itself is more than 30 in above grade, so its open edges need a guard at least 36 in high (R312.1.1 and R312.1.2). The treads are a closer call. On level ground the top tread sits 28.8 in up — four risers of 7.2 in — just under the 30 in guard trigger, so the stair usually needs a handrail but not a guard. If the yard falls away beside the stair, measure again.
Each stringer is about 55 in long, so the stock line lists one 8 ft 2×12 per stringer; the offcut is too short for a second stringer once you allow for the top and bottom cuts. A 36 in wide stair at 16 in maximum spacing takes four stringers. The 2×12 keeps about 5.3 in of solid wood below each notch — the throat — which clears the 5 in minimum in DCA 6 (Figure 28).
The usual mistake at this height is measuring from the deck down to the lawn right at the house wall. The bottom step lands 42 in (3½ ft) out, and ground is normally graded to fall away from a house, so the real rise at the landing is often an inch or two more. That extra lands entirely on the bottom riser. Set or pour the landing pad first, then measure from the deck surface to the pad with a level straightedge.
Six inches lower, How many steps for a 30 in deck drops to four risers of exactly 7½ in, and a foot lower, How many steps for a 2 ft deck to four of 6 in; a foot higher, How many steps for a 4 ft deck is where the stair needs its own guard. The deck railing at this height is laid out on How many balusters for a 6 ft railing section.
Different size? Use the full Stair Stringer Calculator.
What you’ll need
- Framing squareBudget price
The tool for laying out stair stringers and rafters: rise on one leg, run on the other.
See options on Amazon (opens in a new tab) - Stair gaugesBudget price
Small brass or steel buttons that clamp to a framing square so every rise and run you mark is identical.
See options on Amazon (opens in a new tab) - Circular saw (7¼ in)Mid-range price
The most versatile first power saw: crosscuts framing lumber, rips boards and, with a straightedge, breaks down plywood sheets.
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Frequently asked questions
How long is the stringer for a 36 in deck rise with 11 in treads?
About 56-7/8 inches (4 ft 8-7/8 in) along the slope, with 44 inches (3 ft 8 in) of total run. At 11 inches the IRC no longer requires a nosing (R311.7.5.3), and 2 × riser + tread comes to 25.4 in, inside the 24–26 in comfort range.
How many stringers for a 5 ft wide stair off a 3 ft deck?
5 stringers at a 16 inch maximum spacing — 5 × 2×12 × 8 ft. The riser and tread layout stays the same; only the stringer count grows with width.
Other common sizes
- How many steps for a 2 ft deck — 4 risers
- How many steps for a 30 in deck — 4 risers
- How many steps for a 4 ft deck — 7 risers
- Stair stringers for an 8 ft rise — 13 risers
- Stair stringers for a 2.7 m rise — 15 risers
Sources
- International Code Council, 2021 International Residential Code, Chapter 3 Building Planning (opens in a new tab) — R311.7.1 width (36 in), R311.7.2 headroom (6 ft 8 in), R311.7.3 vertical rise of a flight (12 ft 7 in), R311.7.5.1 risers (7¾ in; open risers more than 30 in up must not pass a 4 in sphere), R311.7.5.2 treads (10 in), R311.7.5.3 nosings (¾–1¼ in unless the tread is 11 in or deeper), R311.7.6 landings (36 in deep), R311.7.8 handrails, R312.1 guards.
- American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide (2015 IRC edition) (opens in a new tab) — Stair requirements, Figures 28, 29, 31 and 34: 2×12 minimum stringers; cut stringers span no more than 6 ft 0 in and keep at least 5 in below the notches; at least three cut stringers at no more than 18 in on center; sloped hangers or a hanger board at the top; an intermediate landing where the total rise exceeds 12 ft; stringers bear on footings below frost depth, not on pads or patios that aren’t founded that deep.