What size stringer do I need for a deck stair?

2×12 PT is the contractor default for cut/notched stringers because it leaves a healthier 'throat' (residual web below the deepest notch) — AWC DCA-6 requires throat ≥ 5″. For a typical 7″ riser cut into a 2×12 (11.25″ depth), throat is 11.25 − 7 = 4.25″ — actually FAILS. To pass, either (a) drop riser to ≤ 6.25″ by adding one more riser (lower total rise per step), or (b) use solid-stringer style with cleats (no notch, full 11.25″ retained). 2×10 cut stringers only work for low risers (≤ 4″) — rare on residential decks.

How long does a stair stringer need to be?

Length = √(totalRise² + totalRun²) — pure right-triangle hypotenuse. For 42″ rise + 55″ run (5 treads × 11″): √(42² + 55²) = √(1,764 + 3,025) = √4,789 ≈ 69.2″ or 5′-9.2″. Buy 8′ stock and trim — gives 6.8″ of cut waste, plenty for the top + bottom miter and seat cuts. DeckMath auto-rounds up to the next stock length (8/10/12/14/16 ft).

How many stringers do I need for a 42-inch wide stair?

For cut/notched stringers (16″ o.c. max spacing per AWC DCA-6): ceil(42/16) + 1 = 4 stringers. For solid/cleated stringers (24″ o.c. max): ceil(42/24) + 1 = 3 stringers. Cut stringers need tighter spacing because notching removes ~40% of the cross-section. Wider stairs scale proportionally — 48″ cut needs 5 stringers, 60″ cut needs 5, 72″ cut needs 6.

What is stringer throat depth and why does it matter?

Throat depth = remaining lumber web BELOW the deepest notch cut into a cut/notched stringer. AWC DCA-6 (the IRC's referenced deck guide) requires throat ≥ 5 inches. A 2×12 (11.25″ deep) with a 7″ riser notch leaves 4.25″ — FAILS. The throat carries the entire structural load (the notched portion has zero strength), so insufficient throat = stringer buckles under load. Fixes: bigger lumber, smaller riser, or switch to solid-stringer style (no notch).

Cut stringer vs solid stringer — which is better?

Cut/notched: easier to lay out (framing square + carpenter pencil + circular saw), traditional look, no exposed hardware. Drawbacks: notching removes 40-50% of lumber strength, requires careful throat math, more stringers needed (16″ o.c. max). Solid w/ cleats: full lumber strength retained, fewer stringers (24″ o.c. ok), exposed metal cleats visible from below. More material-efficient overall but more hardware. Modern code-conscious DIY → solid. Traditional aesthetic → cut.

Should stringers be hung or rested on the deck?

Hung: stringer top face-mounts to the deck rim with a Simpson LSCZ stringer hanger (1 per stringer, 8 × SDS screws each, ~$14.50/bracket). Stringer bottom doesn't extend above deck — cleaner finish, allows drainage gap. Rested: stringer is notched at the top so it sits ON the deck rim, with the deck edge tucking into the cutout. No bracket needed but stringer must be 1.5″ deeper than the notch, and the visible stringer top breaks the clean deck-edge line. Most modern contractors use hung-style.

What's the stringer angle for a typical deck stair?

θ = atan(rise / run). For 7″ rise + 11″ run (IRC-comfort default): atan(7/11) = 32.5° from horizontal. IRC-recommended comfort band is 30-38°. Steeper than 38° (rise/run > 0.78) feels like a ladder; shallower than 30° (rise/run < 0.58) wastes horizontal space. Most code-compliant deck stairs land at 32-36°.

Do I need pressure-treated lumber for stringers?

Yes — IRC 2021 R317.1 requires PT for any wood within 6″ of grade. Stringer bottoms sit on the landing pad, often soaked by rain runoff, so PT (UC4A ground-contact rated) is mandatory not optional. PT standard (SYP #2, 25-yr rot warranty) costs $3.20-$4.10/lf. PT premium (Yellawood / MicroPro / Wolmanized AC2) adds 28% for a lifetime warranty + cleaner chemistry that doesn't corrode standard galvanized fasteners as fast — worth it on a part that gets soaked.

Can I use 2×10 for stair stringers instead of 2×12?

Sometimes — but the math has to work. 2×10 (9.25″ depth) with a 7″ riser notch leaves a 2.25″ throat — FAILS AWC DCA-6's 5″ minimum. 2×10 only passes when riser height is ≤ 4.25″ (rare on residential decks) OR when style = solid (no notch, full 9.25″ retained). For 99% of deck stairs, use 2×12 cut OR 2×10 solid. DeckMath flags the failing combo and recommends the cheapest passing alternative.

How many bottom-fasteners per stringer do I need?

Hung stringers: 8 Simpson SDS 1/4″ × 1-1/2″ structural screws per LSCZ bracket (per Simpson's allowable-load chart) — bracket attaches to deck rim. Plus a general kit (~10 deck screws, framing nails) per stringer for tread + riser attachment. Rested stringers: no bracket, but each stringer needs 2 × 6″ structural screws toe-screwed through the notched seat into the deck rim, plus the general kit. Bottom of stringer attaches to landing pad with a steel angle + 1/2″ × 4″ wedge anchors (1-2 anchors per stringer).

stairs · stringer cut layout · IRC R311.7 + AWC DCA-6

Stair Stringer Calculator

Q: Do I need pressure-treated lumber for stringers?

Yes — IRC 2021 R317.1 requires PT for any wood within 6″ of grade. Stringer bottoms sit on the landing pad, often soaked by rain runoff, so PT (UC4A ground-contact rated) is mandatory not optional. PT standard (SYP #2, 25-yr rot warranty) costs $3.20-$4.10/lf. PT premium (Yellawood / MicroPro / Wolmanized AC2) adds 28% for a lifetime warranty + cleaner chemistry that doesn't corrode standard galvanized fasteners as fast — worth it on a part that gets soaked.

Q: Can I use 2×10 for stair stringers instead of 2×12?

Sometimes — but the math has to work. 2×10 (9.25″ depth) with a 7″ riser notch leaves a 2.25″ throat — FAILS AWC DCA-6's 5″ minimum. 2×10 only passes when riser height is ≤ 4.25″ (rare on residential decks) OR when style = solid (no notch, full 9.25″ retained). For 99% of deck stairs, use 2×12 cut OR 2×10 solid. DeckMath flags the failing combo and recommends the cheapest passing alternative.

Q: How many bottom-fasteners per stringer do I need?

Hung stringers: 8 Simpson SDS 1/4″ × 1-1/2″ structural screws per LSCZ bracket (per Simpson's allowable-load chart) — bracket attaches to deck rim. Plus a general kit (~10 deck screws, framing nails) per stringer for tread + riser attachment. Rested stringers: no bracket, but each stringer needs 2 × 6″ structural screws toe-screwed through the notched seat into the deck rim, plus the general kit. Bottom of stringer attaches to landing pad with a steel angle + 1/2″ × 4″ wedge anchors (1-2 anchors per stringer).

Stringer hypotenuse, notch depth, residual throat (DCA-6 ≥ 5″ enforced), stock-length pick, stringer count + spacing, Simpson LSCZ bracket + SDS fastener schedule, and full BoM. Every dimension cross-validated against IRC 2021 R311.7 — riser ≤ 7.75″, run ≥ 10″, width ≥ 36″ — and AWC DCA-6's throat-depth rule. Cut vs solid styles, hung vs rested attachment, 2×10 / 2×12 lumber. Pairs with deck-stair-calculator (full-stair BoM) and stair-rise-run-calculator (pure geometry).

IRC R311.7DCA-6 throat ≥ 5″Cut + solid stylesHung + rested attachmentFull BoM

5″·Min throat (DCA-6)

7.75″·IRC max rise

30-38°·Comfort angle band

16/24″·Cut / solid spacing

Inputs

Stair dimensions

Total risedeck-to-grade

Stair widthclear width

Tread runIRC ≥ 10″

Nosingclosed-riser overhang

Risers / treads6 / 5

Rise per step7″ ✓

Total run55″

Hypotenuse69.2″ (8′ stock)

Angle37.4°

Stringer style

Attachment

Lumber size2×12 leaves better throat

Material tier

State2-letter

Results

⚠ Check compliance below · cut stringer · hung from rim

Stringer count

8′ stock each

Hypotenuse

37.4° angle

Throat depth

2x12 − 7″ notch

Project total

Low $492 · Northeast

Stringer side elevation — cut/notched profile

2x12 stringer (11.25″) hypotenuse 69.2″throat 4.25″ ⚠

Riser height 7″ ≤ IRC max 7.75″

IRC R311.7.5.1

Each of the 6 risers is exactly 7″. IRC R311.7.5.1 caps risers at 7-3/4″ and requires every riser equal within 3/8″.

Tread run 11″ ≥ IRC min 10″

IRC R311.7.5.2

Each tread is 11″ deep with 1″ nosing projection (closed-riser). IRC R311.7.5.2 requires 10″ minimum tread depth; 11″ is the contractor sweet-spot for comfort.

Stair width 42″ ≥ IRC min 36″

IRC R311.7.1

Clear stair width must be at least 36″ between handrails (R311.7.1). Most deck stairs are 36-48″.

Throat depth 4.25″ FAILS DCA-6 min 5″

AWC DCA-6

2x12 (11.25″ deep) − 7″ riser notch leaves only 4.25″ web. Options: upgrade to 2×12 (adds 0.00″ throat), reduce riser height by adding more risers, or switch to solid-stringer style (no notch).

4 stringers at 16″ o.c.

AWC DCA-6

Cut stringers require ≤ 16″ spacing per AWC DCA-6 (notched cross-section is ~40% weaker). For 42″ width: ceil(42/16) + 1 = 4 stringers, each 8′ stock.

Hung attachment — 4 × Simpson LSCZ + 32 SDS screws

Simpson Strong-Tie spec

Each stringer face-mounted to deck rim with one LSCZ bracket (8 × 1/4″ SDS structural screws per bracket per Simpson allowable-load spec). Total fasteners: 32.

Stringer angle 37.4° — comfort band 30-38°

IRC R311.7 comfort guidance

Angle = atan(42/55) = 37.4°. IRC-recommended comfort band is 30-38°. Steeper = ladder-like; shallower = wastes horizontal space.

Throat 4

DeckMath validation

Throat 4.25″ falls below AWC DCA-6 minimum of 5″ on cut 2x12 with a 7″ riser notch. Switch to 2×12 (throat becomes 4.25″) or use solid-stringer style with cleats.

Item

Qty

Total

2x12 PT standard — SYP #2 UC4A stringers

4 pcs × 8′ stock = 32 lf · 69.2″ hypotenuse needed · notched / sawn-out for treads · 16″ o.c.

4.0 × 8′

$131

2x12 PT standard — SYP #2 UC4A stringers

4 pcs × 8′ stock = 32 lf · 69.2″ hypotenuse needed · notched / sawn-out for treads · 16″ o.c.

4.0 × 8′

—

$131

Simpson LSCZ stringer brackets

4 brackets · 1 per stringer at deck-rim attachment · galvanized · concealed face-mount

4.0 each

$58

Simpson LSCZ stringer brackets

4 brackets · 1 per stringer at deck-rim attachment · galvanized · concealed face-mount

4.0 each

—

$58

Simpson SDS structural screws (1/4″ × 1-1/2″)

32 screws · 8 per LSCZ bracket per Simpson spec · allowable-load rated

32 ea

$18

Simpson SDS structural screws (1/4″ × 1-1/2″)

32 screws · 8 per LSCZ bracket per Simpson spec · allowable-load rated

32 ea

—

$18

Per-stringer fastener kit (deck screws + framing nails)

4 kits · misc structural screws + N10D nails for tread/riser attachment

4.0 kit

$18

Per-stringer fastener kit (deck screws + framing nails)

4 kits · misc structural screws + N10D nails for tread/riser attachment

4.0 kit

—

$18

Materials subtotal

$225

Cost breakdown

Materials (stringers + brackets + fasteners): $207 – $225
Labor (cut + assemble + install): $285 – $349
Subtotal: $492 – $574
Contingency (6%): $34
Project total: $492 – $608

2026-Q1 retail pricing for #2 SYP PT UC4A stringers, Simpson LSCZ brackets, SDS structural screws. Stringer LABOR ONLY — does NOT include treads, risers, handrail, or landing pad (use Deck Stair Calculator for full stair build). Regional labor adjusted for Northeast.

How to use

Three steps. Permit-ready output.

Enter total rise + stair width

Total rise = top-of-deck to bottom-landing surface (typically the concrete pad or paver). Measure with a level — don't approximate. Standard residential stair widths are 36″ (IRC min), 42″ (most common deck), or 48″ (extra-wide / accessible). Cut to the OUTSIDE face of the outer stringers.

Pick tread run + nosing

Tread run is the horizontal depth of each step (excluding nosing overhang). IRC R311.7.5.2 requires 10″ minimum — 11″ is the contractor sweet-spot (comfortable + uses a 2×12 tread + 1″ nosing efficiently). Nosing projects past the riser face by 3/4″–1-1/4″ (closed-riser only). Set nosing to 0 for open-riser stairs.

Cut vs solid stringer style

Cut (notched): saw out tread + riser cuts directly in the stringer. Most common DIY style, easiest to lay out with a framing square. Solid (cleated): no notches — metal angle cleats bolt to the stringer face, treads rest on cleats. Stronger (no weakened throat), uses less lumber but more hardware. DeckMath spaces cut stringers 16″ o.c. and solid stringers 24″ o.c. since notched stringers are structurally weaker.

Hung vs rested attachment

Hung: top of stringer face-mounted to the deck rim with Simpson LSCZ brackets (1 per stringer, 8 SDS structural screws each). Cleaner look, drainage clearance. Rested: stringer notched-in over the deck rim — stringer top sits ON the rim, no brackets needed. Stringer must be 1.5″ deeper than the cut to span the rim. DeckMath returns the bracket count + fastener count for hung; zero for rested.

Lumber size + material tier

2×12 (11.25″ deep) is the contractor default for cut stringers — leaves a healthier throat after notching. 2×10 (9.25″) works only when tread run is small (10–10.5″) so throat stays above the 5″ AWC DCA-6 minimum. Material tier: PT std (SYP UC4A) is the workhorse. PT premium (Yellawood / MicroPro / Wolmanized) adds 28% for a 40-yr-warranty stringer — worth it since stringer bottom soaks up landing-pad rainwater.

How we calculate

The math, fully transparent.

The Stair Stringer Calculator returns the cut layout, stock-length pick, stringer count, and full BoM for a deck stair stringer assembly — sized to your total rise + width + chosen run. Pick cut/notched stringers (most common DIY) or solid w/ steel cleats (less material, stronger), 2×10 vs 2×12 lumber, hung-in-brackets vs rested-on-rim attachment, and PT std vs lifetime-warranty premium. DeckMath cross-validates every dimension against IRC 2021 R311.7 — riser height ≤ 7.75″, tread run ≥ 10″, width ≥ 36″ — plus AWC DCA-6's throat-depth rule (residual web ≥ 5″ below the deepest notch). Failing combos flagged with the cheapest passing alternative. Pairs with deck-stair-calculator (Phase 1, full-stair BoM) and stair-rise-run-calculator (W9.2, pure-geometry sizing).

IRC references

IRC 2021 R311.7.5.1 — Riser height: 7-3/4″ max, every riser equal within 3/8″
IRC 2021 R311.7.5.2 — Tread depth: 10″ minimum
IRC 2021 R311.7.5.3 — Nosing: 3/4″-1-1/4″ projection on closed-riser stairs
IRC 2021 R311.7.1 — Stair width: 36″ minimum between handrails
IRC 2021 R311.7.3 — Single flight max: 12′ vertical rise before intermediate landing
AWC DCA-6 2015 — Stringer throat depth ≥ 5″ after notch (cut stringers)
AWC DCA-6 — Cut-stringer max spacing 16″ o.c.; solid-stringer up to 24″ o.c.

2026-Q1 retail pricing for #2 SYP PT UC4A stringers — 2×10 $3.20/lf, 2×12 $4.10/lf. PT premium (Yellawood / MicroPro Sienna / Wolmanized AC2) 1.28× std. Simpson LSCZ brackets $14.50 each, 8 × 1/4″ SDS structural screws per LSCZ per Simpson allowable-load chart. Stringer depth: 2×10 = 9.25″, 2×12 = 11.25″. Span rules: cut stringers ≤ 16″ o.c., solid stringers ≤ 24″ o.c. per AWC DCA-6 2015.

Riser count + height

risers = ceil(totalRise / 7.75); riseEach = totalRise / risers

Minimize riser count subject to IRC R311.7.5.1 (≤ 7.75″). 42″ total → ceil(42/7.75) = 6 risers @ exactly 7.00″ each. Every riser must be equal within 3/8″ per R311.7.5.1.

Tread count + total run

treads = risers − 1; totalRun = treads × treadRunIn

The top step is the deck edge, so treads = risers − 1. 6 risers → 5 treads × 11″ run = 55″ total run.

Stringer hypotenuse

L = √(totalRise² + totalRun²)

Right-triangle hypotenuse from rise + run. 42″ rise + 55″ run → √(1,764 + 3,025) = √4,789 = 69.2″ ≈ 5′-9.2″. Round up to next stock size (8′) and add 6″ for cut waste.

Stringer count

count = max(2, ceil(width / spacing) + 1)

Cut stringers at 16″ o.c., solid at 24″ o.c. (cut stringers are structurally weaker so need more of them). For 42″ wide cut: ceil(42/16) + 1 = 4 stringers. For 42″ solid: ceil(42/24) + 1 = 3 stringers.

Throat depth (cut stringers only)

throat = lumberDepth − riserHeight

2×12 (11.25″) − 7.00″ riser = 4.25″ throat — FAILS AWC DCA-6 5″ minimum. Either widen to 2×12 + reduce riser (7.00″ → 6.25″ by adding a riser), or switch to solid-stringer style.

Stringer angle

θ = atan2(totalRise, totalRun) × 180/π

42″ rise / 55″ run → 37.4° from horizontal. IRC-recommended comfort band is 30-38°. Above 38° = steep / harder to descend; below 30° = wastes horizontal space.

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Deck Stair Calculator

Risers, treads, stringer hypotenuse, and BoM for any deck height — IRC 2021 R311.7 compliant with auto handrail + landing-pad sizing.

Stair Rise and Run Calculator

Equal-rise riser distribution, run depth, stringer hypotenuse, and angle for any deck height. IRC R311.7.5 + Blondel 2R + T ergonomic check. Permit-ready callout sheet.

Stair Tread Calculator

Tread board count, total LF + waste, riser boards, fasteners — across 6 materials (PT, composite, Ipe, Cumaru, cedar). IRC R311.7.5 cross-validated.