Stair Tread Calculator
Tread board count, total LF + waste, riser-board count, and material-tier price comparison across 6 deck-stair materials: PT lumber, grooved + square-edge composite, Ipe + Cumaru hardwoods, and cedar. Pick board pattern (single 2×12, two-board 2×6×2, or pre-bullnosed stair-tread stock) and stringer style (cut adds 15% waste, solid 5%). Every tread + nosing cross-validated against IRC 2021 R311.7.5.2 + R311.7.5.3. Pairs with stair-stringer-calculator (cut layout) and stair-rise-run-calculator (pure geometry).
Inputs
Stair dimensions
Results
IRC R311.7.5 compliant · Pressure-treated 5/4 or 2× (SYP) · 18-yr life
Tread run 11″ ≥ IRC min 10″
IRC R311.7.5.2Each tread is 11″ deep (run only, excluding nosing). Effective foot-room = 12″ including 1″ nosing. IRC R311.7.5.2 requires 10″ minimum tread depth.
Nosing 1″ in IRC range 3/4-1.25″
IRC R311.7.5.3Nosing of 1″ falls within IRC R311.7.5.3's required 3/4″-1-1/4″ projection for closed-riser stairs.
6 tread boards × 8′ stock
AWC DCA-6 tread requirements20.1 lf of Pressure-treated 5/4 or 2× (SYP) including 15% waste for cut stringer cuts. 1 board per tread row × 5 treads.
5 riser boards (1×8 PT)
AWC DCA-6 riser standard17.5 lf of 1×8 PT riser stock. Closed-riser style per IRC R311.7.5 (riser blocks debris, hides framing, allows full nosing compliance).
Material comparison — same stair, every material
| Material | $/lf | Treads $ | Lifespan |
|---|---|---|---|
| Pressure-treated 5/4 or 2× (SYP)selected | $2.95 | $59 | 18 yr |
| Western red cedar 2× | $4.20 | $85 | 22 yr |
| Composite grooved (Trex / TimberTech / Fiberon) | $6.50 | $131 | 30 yr |
| Composite square-edge (face-screwed) | $6.85 | $138 | 30 yr |
| Brazilian Cumaru (Brazilian teak) | $8.95 | $180 | 50 yr |
| Brazilian Ipe (Lapacho) | $11.50 | $231 | 75 yr |
Treads-only cost across all 6 materials — pick the right tier for your budget + lifespan target. Hardwoods cost 4× PT but last 4× longer with zero stain/seal maintenance.
Cost breakdown
- Materials (treads + risers + fasteners)
- $99 – $108
- Labor (cut + fasten + nose)
- $99 – $121
- Subtotal
- $198 – $229
- Contingency (6%)
- $14
- Project total
- $198 – $242
2026-Q1 retail pricing. TREADS ONLY — does NOT include stringers (use Stair Stringer Calculator), handrail, or landing pad (use Deck Stair Calculator for full stair BoM). Regional labor adjusted for Northeast.
How to use
How to use the stair tread calculator in 5 steps.
- 1
Enter tread count + stair width
Tread count = riser count − 1 (top step is the deck edge). For a 36″ deck → 5 risers → 4 treads; 42″ deck → 6 risers → 5 treads; 48″ → 7 risers → 6 treads. Use the Stair Rise & Run Calculator first if you don't know your riser count. Stair width is the clear distance between stringer outer faces — 36″ IRC min, 42-48″ most common.
- 2
Pick run + nosing
Tread run is the horizontal depth (excluding nosing) — IRC ≥ 10″. 11″ is the contractor sweet-spot. Nosing projects past the riser face by 3/4″-1-1/4″ on closed-riser stairs (R311.7.5.3). Effective tread depth = run + nosing, so 11″ + 1″ = 12″ of foot-room.
- 3
Choose tread material
PT lumber ($2.95/lf): cheapest, 18-yr life, fits 8/10/12/16 ft stock. Composite grooved ($6.50/lf): 30-yr warranty, hidden-clip fastening, 12/16/20 ft. Composite square-edge ($6.85/lf): face-screwed + plugs. Ipe ($11.50/lf, 75 yr) + Cumaru ($8.95/lf, 50 yr): premium hardwoods, stunning grain, ages to silver if unsealed. Cedar ($4.20/lf, 22 yr): visual upgrade over PT, mid-tier.
- 4
Board pattern
Single-board: one 11.25″ board (2×12 nominal) — clean look, works to 48″ wide. Two-board: 2 × 5.5″ boards (2×6 + 2×6) — standard for wider stairs (> 48″), more stable, mimics deck board patterning. Stair-tread stock: pre-bullnosed 12″ wide board — eliminates nosing build-up, premium look, only available in PT + Ipe.
- 5
Risers + stringer style
Include risers: closed-riser style (riser board behind each tread). Skip risers for open-riser (skip-stop) style — visible from below, requires open spacing ≤ 4″ per IRC R312.1.3.1. Stringer style affects waste: cut stringers (notched) leave 15% scrap from tread cuts, solid stringers (cleated) only 5% trim waste. DeckMath bumps tread LF accordingly.
How we calculate
How DeckMath calculates this — IRC 2021 sources.
The Stair Tread Calculator returns the tread lumber BoM for a deck stair: board count by stock length, total LF + waste factor, riser-board count, fasteners, and side-by-side cost comparisons across six materials (PT lumber, grooved + square-edge composite, Ipe + Cumaru hardwoods, cedar). Pick tread count, stair width, run, nosing, and board pattern (single 11.25″ board, two-board 2×6+2×6, or pre-bullnosed stair-tread stock). DeckMath enforces IRC R311.7.5.2 (10″ min run) + R311.7.5.3 (nosing 3/4″-1-1/4″) and adds the right waste factor for cut vs solid stringers (15% vs 5%). Pairs with stair-stringer-calculator (cut-layout BoM), stair-rise-run-calculator (pure geometry), and deck-stair-calculator (full stair BoM).
IRC references
- 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 R311.7.5.3.1 — Nosing of treads must comply with slip-resistance
- IRC 2021 R312.1.3.1 — Open-riser stairs: 4″ sphere can't pass through opening
- IRC 2021 R317.1 — Pressure-treated lumber required within 6″ of grade
- AWC DCA-6 — Tread board minimum thickness 1-1/16″ (5/4 deck board) for ≤ 16″ stringer spacing
2026-Q1 retail pricing: PT lumber 5/4×6 $2.95/lf · composite grooved $6.50/lf · composite square-edge $6.85/lf · Brazilian Ipe $11.50/lf · Cumaru $8.95/lf · western red cedar $4.20/lf. Stock-length availability varies — PT/cedar 8/10/12/16 ft, composite 12/16/20 ft, hardwoods 6/8/10/12 ft. Waste factor: cut/notched stringers 15% (notched-cut tread offcuts), solid stringers 5% (trim only). Riser boards 1×8 PT $1.85/lf. Fastener kits 1/tread — hidden clips + plugs for composite, stainless screws + pilot bit for hardwood, deck screws for PT/cedar.
Stair width converted to feet × boards per tread row. 42″ wide × 1 board (single-board pattern) = 3.5 lf per tread. 42″ × 2 (two-board) = 7 lf.
Cut stringers waste 15% from notched-cut tread offcuts; solid stringers waste 5%. For 5 treads × 3.5 lf × 1.15 (cut) = 20.1 lf order. Solid: 5 × 3.5 × 1.05 = 18.4 lf.
Assumes one stock board cuts down to one tread board (most efficient when stair width ≤ stock length). 5 treads × 1 board × 1.15 = 5.75 → 6 boards needed. Pick stock = next stock length ≥ stair width — 42″ width → 4 ft? No — 8 ft is the smallest commonly stocked.
Closed-riser: 1 riser board per tread row, same width as the stair. 5 treads × 3.5 ft = 17.5 lf of 1×8 riser stock.
What your foot actually steps on: 11″ run + 1″ nosing = 12″ of foot-room. Open-riser stairs have no nosing, so effDepth = run = 11″ (still IRC-compliant, but feels slightly less roomy).
Save your plan
Don’t lose this estimate.
Your inputs are preserved in the URL — email it to yourself or copy the link so you can compare with contractor bids later. No account needed.
Get matched
Want 2–3 free quotes for this exact deck?
We'll send your plan to vetted local builders. Free, no obligation.
People also ask
Stair tread questions, answered.
(1) Find tread count = riser count − 1. (2) Per-tread board LF = (stair width in ft) × (boards per tread). 42″ wide × 1 board (single-board) = 3.5 lf. (3) Total LF = per-tread LF × tread count × waste factor (1.15 for cut stringers, 1.05 for solid). 5 treads × 3.5 × 1.15 = 20.1 lf order. (4) Stock board count = ceil(treadCount × boardsPerTread × waste). 5 × 1 × 1.15 = 5.75 → 6 boards. Add riser boards (1×8 PT) if closed-riser style: 5 × 3.5 = 17.5 lf riser stock.
Best value: Composite grooved (Trex Transcend, TimberTech AZEK, Fiberon Sanctuary) — $6.50/lf, 30-yr warranty, hidden-clip fastening (clean look), no maintenance, slip-rated 'good'. Best longevity: Brazilian Ipe — $11.50/lf, 75-yr life, hardest commercial decking wood (4× harder than oak), ages to silver. Best budget: PT 5/4×6 or 2×6 — $2.95/lf, 18-yr life with annual sealing. Mid-tier hardwood: Cumaru — $8.95/lf, 50-yr life, 25% cheaper than Ipe with similar density.
Composite — when you want zero maintenance, can pay $6.50-7/lf upfront, and prefer a uniform color/texture across the deck. 30-yr warranty, never needs staining/sealing, slip-rated good with texturized surface. Wood (PT or hardwood) — when budget is tight (PT) or you want a high-end natural look (Ipe/Cumaru). PT requires re-staining every 2-3 years; Ipe ages to silver if unsealed (most people prefer this). Cedar is a middle-ground softwood but NOT ground-contact, so stringers must be PT.
5/4 deck board (1.0625″ actual) is the minimum AWC DCA-6 standard for treads when stringers are spaced ≤ 16″ o.c. (the cut-stringer standard). 2× lumber (1.5″) is allowed and arguably preferred — adds rigidity, less bounce, slightly more material cost (+15-20%). For wider stringer spacing (≥ 24″, solid-stringer style), 2× lumber is required — 5/4 will sag under load. Composite + hardwood treads typically come 1″ thick (matches deck-board lines) and are rated for any stringer spacing.
11.25″ (single 2×12 nominal): cleanest look, fits 11″ run + 1″ nosing exactly. Works to 48″ stair width. Two-board pattern (2 × 5.5″ each, 2×6 nominal × 2): standard for wider stairs, more stable across span, mimics deck-board pattern aesthetic. Pre-bullnosed stair-tread stock (12″ wide, factory radius nosing): premium look, no separate nosing build-up needed — but limited to PT lumber and Ipe at most yards.
Closed-riser stairs (with riser board behind each tread) — code default per IRC R311.7.5. Riser blocks debris from falling through, gives a finished look, allows full nosing compliance (3/4″-1-1/4″). Open-riser stairs — allowed only if 4-inch sphere cannot pass through the open space between treads (R312.1.3.1). This is rare for residential decks since most stair geometries leave 6-8″ open. Closed-riser is the safe code-default choice.
Cut/notched stringers: 15% extra lumber. The notched cuts in the stringer leave 1-2″ unusable scrap from each tread board. Solid stringers (with cleats): 5% extra. Treads bolt straight to cleats, only trim waste at ends. DeckMath's waste factors are conservative and assume professional cuts — DIY cuts can run 20%+ for cut stringers. Always round UP to the next whole stock board.
PT lumber: 8 ft is the smallest commonly stocked. For 42″ stairs (3.5 ft wide), buy 8 ft → 1 tread per board (lots of waste) OR buy 16 ft → 4 treads per board (lots of cuts). DeckMath picks the next stock length ≥ stair width — usually 8 ft minimum. Composite: 12/16/20 ft only — pick to minimize waste (e.g. 16 ft → 4 treads per board × 42″ wide = 4 × 3.5 = 14 ft used, 2 ft scrap = 12.5% waste). Hardwoods: 6/8/10/12 ft — shorter stock, order more boards.
PT lumber treads: 3-3.5″ exterior deck screws (Spax PowerLags or Simpson Strong-Drive), 2 per stringer per board. Pre-drill near ends to prevent splitting. Composite grooved: hidden clips (CAMO Marksman or TigerClaw) screwed into stringer groove — clip slides into board side groove. Composite square-edge: 3″ stainless deck screws + color-matched plugs (CAMO Hex Plugs). Hardwood: stainless screws ONLY (carbon-steel rusts at the Ipe phenol-tannin contact), pre-drilled pilot holes mandatory (Ipe is 4× harder than oak — splits regular screws).
PT lumber: 18 yrs with annual sealing/staining; 12 yrs un-maintained (silver-grey weathering, eventual checking). Cedar: 22 yrs (natural oils slow rot). Composite (Trex/TimberTech): 25-30 yrs (manufacturer warranty 25-30 yrs against rot/fading/splintering — actual life often longer). Hardwood Ipe: 50-75 yrs (the longest-lasting deck material commonly available — natural Class A fire rating). Cumaru: 50 yrs. Maintenance: PT + cedar need annual seal/stain; composite + hardwood need only a power-wash 1× per year.
Embed this calculator
One line. Any site. Free.
Drop the snippet into your contractor site, blog, or marketing page. Theme matches the parent site automatically.
<!-- Stair Tread Calculator — free embed by DeckMath --> <a href="https://deckmath.com/calculators/stair-tread-calculator" data-deckmath-calc="stair-tread-calculator" data-theme="auto">Free Stair Tread Calculator by DeckMath</a> <script src="https://embed.deckmath.com/v1.js" async></script>
Plan the whole project, not just one number
The Deck Project Planner turns your dimensions into a complete material list, cost, 3D preview, and a PDF you can take to the lumber yard — all in one place.
Related