Stair stringers for a 4 ft (48 in) high deck
A 4 ft (48 in) high deck needs 7 risers of 6-7/8 inches and 6 treads. At 10½ inches per tread that is 63 inches (5 ft 3 in) of run and a stringer about 79-3/16 inches (6 ft 7-3/16 in) long.
How to work it out
- 48 in ÷ 7.75 in max = 6.19 → round up to 7 risers, each 48 in ÷ 7 = 6-7/8 in scant (6.86 in)
- 6 treads × 10-1/2 in = 63 in run · √(48² + 63²) = 79-3/16 in along the slope
- Comfort check: 2 × 6-7/8 in + 10-1/2 in = 24.2 in (24–26 in is comfortable) · stair angle 33.1 degrees
- Throat: 11-1/4 in board − 5.74 in notch depth = 5-1/2 in
- Tread board: 10-1/2 in tread + 3/4 in nosing + 0 in riser board = 11-1/4 in
- Top level cut: 6-7/8 in riser + 1 in tread = 7-7/8 in below the deck surface
Six risers would be 8 in each — over the 7¾ in limit — so the flight goes to seven gentler steps. That adds a tread, and the stairs now reach about 5¼ ft out from the deck, plus you need a clear landing at the bottom.
Adjust for your project
More options: Max riser · Spacing · Stringer board …
- Steps to cut
- 6 steps to cut in each stringer + the deck is the top step
- Total run (how far the stairs reach out)
- 63 in (5 ft 3 in)
- Stringer length (along the slope)
- 79-3/16 in (6 ft 7-3/16 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
- 7-7/8 in
- Wood left below the notches (throat)
- 5-1/2 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 | 12 pieces 36 in long (2 per step) → buy 4 × 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 | 6-7/8 in | — |
| Tread 2 | 13-11/16 in | — |
| Tread 3 | 20-9/16 in | — |
| Tread 4 | 27-7/16 in | — |
| Tread 5 | 34-5/16 in | Yes — over 30 in |
| Tread 6 | 41-1/8 in | Yes — over 30 in |
| Deck surface | 48 in | Yes — over 30 in |
One step fewer or more
| Risers | Each step | Treads | Tread depth | Total run | Check |
|---|---|---|---|---|---|
| 6 risers | 8 in | 5 | 10-1/2 in | 52-1/2 in | Risers too tall |
| 7 risers (shown) | 6-7/8 in | 6 | 10-1/2 in | 63 in | OK |
| 8 risers | 6 in | 7 | 10-1/2 in | 73-1/2 in | OK |
- Each step is marked to the nearest 1/16 in. Stepping off 6-7/8 in 7 times would put the top 1/8 in high, 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.
- Stair guard required from tread 5: it sits more than 30 in above the bottom, so open sides need a guard at least 34 in high (IRC R312.1.1, R312.1.2). This assumes the ground beside the stair is level with the bottom landing — measure where it falls away.
- 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 6-7/8 in as the rest.
Stringers for a 48 in rise, by stair width
| Stair width | Stringers needed | Stringer stock to buy |
|---|---|---|
| 36 in | 4 stringers | 4 × 2×12 × 8 ft |
| 48 in | 4 stringers | 4 × 2×12 × 8 ft |
| 60 in | 5 stringers | 5 × 2×12 × 8 ft |
| 72 in | 6 stringers | 6 × 2×12 × 8 ft |
What to know about stairs for a 4 ft deck
This is the height where the stair itself needs a guard. With 6-7/8 in risers on level ground, the fifth and sixth treads sit about 34.3 in and 41.1 in above grade — over the 30 in trigger in IRC R312.1.1. On the open sides of a stair the guard must be at least 34 in high, measured from the line of the nosings, and its openings may not pass a 4-3/8 in sphere; the triangle under the bottom rail, between tread and riser, gets a 6 in sphere (R312.1.2 and R312.1.3). The deck above needs its own 36 in guard, and seven risers need a handrail too (R311.7.8).
The stringer is about 79 in long, which still comes out of an 8 ft 2×12, but with little to spare once you allow for the plumb cut at the top and the level cut at the bottom. The throat here is about 5.5 in, so pick straight boards without large knots along the lower edge, where the wood is in tension.
Footprint is the other surprise. The 63 in run lands the bottom step more than 5 ft from the deck, and you still need a level landing beyond it. Where the yard is tight, many builders turn the stair to run along the rim; the riser and tread numbers don’t change, only where the flight lands.
For the railing on the stair and the deck, the same spacing rules apply as on How many balusters for an 8 ft railing section. A foot lower, How many steps for a 3 ft deck needs no stair guard on level ground. Indoors, a full storey is on Stair stringers for a 9 ft rise.
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.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How long is a stringer for a 48 in deck with 11¼ in treads?
About 82-13/16 inches (6 ft 10-13/16 in), with 67-1/2 inches (5 ft 7-1/2 in) of total run. An 11¼ inch tread is two 5/4×6 deck boards (5½ in each) with a ¼ in gap, and at 11 inches or deeper the IRC drops the nosing requirement.
How many stringers for 6 ft wide stairs on a 4 ft deck?
6 stringers at a 16 inch maximum spacing — 6 × 2×12 × 8 ft. The handrail rule is per flight, so a wide stair still needs a rail on at least one side.
Other common sizes
- How many steps for a 3 ft deck — 5 risers
- How many steps for a 2 ft deck — 4 risers
- How many steps for a 30 in deck — 4 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.