Plan your deck build — boards, framing, and hardware in one estimate.
By BuildDecide Editorial Team
Before you start
Have your room dimensions ready. All inputs default to common sizes so you can see a worked example instantly.
ft
Longest dimension — boards typically run this direction.
ft
Joists span this direction. 12–16 ft is common for rectangular decks.
in
5.5" = 2×6 nominal. Composite boards are often 5.25–5.5". Use actual width.
in
¼" typical for composite; ⅛"–¼" for pressure-treated. Check manufacturer spec.
in
16" OC is standard. 12" OC for composite on a diagonal; 24" OC sometimes for 2× lumber.
%
Covers cuts, defects, and end-matching. 10% for straight lay; 15% for diagonal or picture-frame.
Deck area19212' × 16' — square footage for decking and railing planning.
Deck boards needed345.5" boards with 0.25" gap — runs across the 16' width.
Linear feet of decking449Includes 10% waste — buy boards that sum to at least this.
Joists needed1016" OC spacing — each joist spans 16 ft. Add double joists at butt joints.
Joist linear feet16010 joists × 16' each. Use 2×8 or 2×10 depending on span — check local span tables.
Deck screws (approx.)6802 per board-joist intersection. Pre-drill composite/hardwood to prevent mushrooming.
What's next?
Boards estimated? Next: <a href="/deck-building-cost/">see 2026 deck building costs</a> for installed pricing, <a href="/compare/composite-vs-wood-decking/">compare composite vs wood decking</a>, or <a href="/concrete-patio-cost/">check concrete patio costs</a> for ground-level alternatives.
Affiliate slot — recommended tools/services
How to estimate deck materials
A deck has two main material systems: decking (what you walk on) and framing (joists, beams, posts underneath). This calculator covers both with basic inputs.
Deck boards
Boards run perpendicular to joists — typically the long direction of the deck. The calculator divides deck width by the effective board coverage (actual width + gap) to get board count, then multiplies by length for total linear feet.
Standard board lengths: 8', 10', 12', 16', 20'. When buying, pick lengths that minimize butt joints. For a 12' deck, buy 12' boards so each run is one piece — no seam.
Worked example: 12×16 ft deck
Area: 12 × 16 = 192 sq ft
With 5.5" boards (2×6) and ¼" gap: 16 ft × 12 in ÷ 5.75 in = 34 boards (rounded up)
Linear feet: 34 × 12 ft = 408 linear ft + 10% waste = 449 ft → buy 28 × 16 ft boards (448 ft) or equivalent
Joists at 16" OC: floor(12 × 12 ÷ 16) + 1 = 10 joists, each 16 ft = 160 linear ft of joist lumber
Standard for most decks — 2× lumber and composite parallel to joists
The default for most builds
24" OC
2×6 or thicker decking only
Not for composite — will feel bouncy; not code in many areas
Composite and PVC decking often requires 12" OC for diagonal installs and 16" OC max for perpendicular — check the manufacturer install guide, not the lumberyard advice.
What this calculator does NOT include
This is a decking + joist-only estimate. A complete build also needs:
Beams — doubled 2×10 or 2×12 under joists, size per span tables
Posts — 4×4 or 6×6, height and footing per local code
Ledger board — 2× lumber attached to house with lag bolts or structural screws
Railing — posts, balusters, top cap — often 15–25% of total material cost
Stairs — stringers, treads, risers, landing pad
Footings — concrete piers below frost line (see our concrete calculator for footing pours)
A rough rule: framing (joists + beams + posts) adds 30–50% to the decking material cost. Railing and stairs add more.
Wood vs composite decking
This calculator works for both — just adjust the gap. Pressure-treated pine typically uses ⅛" gap (it shrinks). Composite uses ¼" gap (it expands in heat). Hidden fastener systems change the effective board width — measure your actual clip spacing.
Decking material is one part of the total bill. For installed pricing including labor, see our deck building cost guide — $25–$90+/sq ft ranges for 2026 depending on material and complexity.
Same dye lot: order all deck boards from the same batch — composite colors shift between production runs
Butt joints over double joists: if you must seam boards end-to-end, place the joint over a doubled joist or blocking
End sealing: pressure-treated cut ends should be field-treated with preservative; composite cut ends are cosmetic
Pre-drill composite: skip pre-drilling and screws mushroom ("volcano") — pre-drilling adds time but looks cleaner on visible decks
Buy screws in bulk: a 1,750-count box of coated deck screws costs $90–$140 vs $15 per 100-count pack — bulk saves 30–50% per screw
Industry benchmarks
Standard joist spacing
16" OC — most decks (2× lumber and composite perpendicular)
Composite diagonal
12" OC required by most manufacturers
Typical gap (wood)
⅛" — PT pine shrinks after install
Typical gap (composite)
¼" — composite expands in heat
Screws per board-joist
2 — top-down or hidden clip systems differ
AdSense slot — in-content
Frequently asked questions
How many deck boards do I need?
Divide deck width (in inches) by the effective board width (actual width + gap), then round up. For a 16 ft wide deck with 5.5" boards and ¼" gap: 16 × 12 ÷ 5.75 ≈ 34 boards. Add 10% waste for cuts and defects.
How far apart should deck joists be?
16" on center is standard for perpendicular decking with 2× lumber and most composite boards. Use 12" OC for composite on a diagonal or when the manufacturer requires it. 24" OC is only acceptable for 2×6 or thicker decking and is not allowed for composite in most jurisdictions.
What size lumber for deck joists?
2×8 or 2×10 depending on span. 2×8 can span up to about 11 ft at 16" OC; 2×10 up to 14 ft. Check your local building code span tables — they vary by species (Southern pine vs SPF vs Douglas fir) and load requirements.
How many screws do I need for a deck?
Budget 2 screws per board-joist intersection. For a 12×16 ft deck with 34 boards and 10 joists: 34 × 10 × 2 ≈ 680 screws. Buy a bulk box — 1,750-count deck screw boxes are common. Add screws for railing, fascia, and stair treads separately.
Should I use 12 ft or 16 ft deck boards?
Match board length to your deck dimension when possible to avoid butt joints. A 12 ft deep deck should use 12 ft boards. A 20 ft wide deck can use two 10 ft boards with the seam over a doubled joist. Fewer seams = cleaner look and fewer moisture entry points.
How much gap between deck boards?
Pressure-treated pine: ⅛" gap (it will shrink as it dries). Composite/PVC: ¼" gap per most manufacturers (it expands in hot sun). Cedar and hardwoods: ⅛"–3/16". Hidden fastener systems have a fixed gap built into the clip — follow the clip spec.
Do I need a permit to build a deck?
Most jurisdictions require a permit for any deck attached to the house or raised above a certain height (commonly 30" above grade). Freestanding ground-level platforms may not need a permit. Check with your local building department — unpermitted decks can cause insurance and resale problems.
Can I use this calculator for a ground-level deck?
Yes. For ground-level (platform) decks, use the same inputs. You may use fewer or shorter posts, and footings may be shallower (check frost depth). Joist and decking math is the same regardless of height. The total project cost will be lower — see our [deck building cost guide](/deck-building-cost/) for ground-level vs raised pricing.
How much does it cost to build a deck?
In 2026, basic pressure-treated decks run $25–$40/sq ft installed. Composite decks range $40–$60/sq ft. Premium builds with exotic hardwood, multi-level designs, or cable railing can exceed $60–$90/sq ft. See our [deck building cost guide](/deck-building-cost/) for full 2026 ranges.