Deck Calculator
A 12×16 ft deck needs about 32 deck boards (5.5"×16 ft), 12 joists (2×8×12 ft), 4 posts, and 2 beams. Materials: $1,500-4,500 depending on wood vs composite.
Deck Calculator
Enter your project dimensions for instant results.
You Need
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How to Calculate Deck Materials
Deck boards: boards = Math.ceil((deck_width_ft × 12) / (board_width_in + gap_in))
Joists: joists = Math.ceil(deck_length_ft / (spacing_in / 12)) + 1
| Material | Cost/sqft | Lifespan | Maintenance |
|---|---|---|---|
| Pressure-treated pine | $2-4 | 10-15 yrs | Stain/seal every 2 yrs |
| Cedar | $4-8 | 15-20 yrs | Seal every 2-3 yrs |
| Redwood | $6-12 | 20-25 yrs | Seal every 2-3 yrs |
| Composite (Trex/TimberTech) | $8-15 | 25-50 yrs | Occasional cleaning |
| PVC (Azek) | $10-18 | 30-50 yrs | Occasional cleaning |
| Decking Type | Joist Spacing | Notes |
|---|---|---|
| 5/4×6 wood (perpendicular) | 16″ OC | Standard residential |
| 5/4×6 wood (diagonal) | 12″ OC | More cuts, more waste |
| 2×6 wood (perpendicular) | 24″ OC | For heavy-duty framing |
| Composite (perpendicular) | 16″ OC | Check manufacturer specs |
| Composite (diagonal) | 12″ OC | Required by most brands |
Hardware Checklist (often forgotten):
- Joist hangers (one per joist connection)
- Post bases (Simpson ABU/ABA series)
- Carriage bolts for beam-to-post connections
- Ledger board lag screws or bolts (code-required pattern)
- Deck screws: ~350 per 100 sq ft (stainless for cedar/composite)
- Flashing tape for ledger board waterproofing
Common Mistakes:
- Not leaving a 1/8" gap between deck boards for drainage and expansion
- Using drywall screws instead of deck screws — they rust and snap
- Attaching the ledger board without proper flashing — the #1 cause of deck rot and house damage
- Skipping concrete footings below frost line — shallow footings heave and shift the entire deck
Frequently Asked Questions
How much does it cost to build a 12x16 deck?
Materials only: $1,500-3,000 for pressure-treated wood, $3,000-6,000 for composite. Professional installation adds $15-35 per square foot. Total installed cost for a 192 sq ft deck: $4,500-10,000 depending on materials, height, and railing complexity.
How many deck boards do I need?
For a 12×16 ft deck with 5.5" wide boards (5/4×6 nominal) and 1/8" gaps: you need about 32 boards at 16 ft length. If using 12 ft boards across the 12 ft width, you need 42 boards. Add 10% for waste from cuts and defects.
How far apart should deck joists be?
16 inches on center for standard 5/4×6 wood decking. 12 inches on center for composite decking installed diagonally, or for 5/4×6 wood installed diagonally. Check your local building code — joist spacing also depends on joist lumber size and span distance.
Do I need a permit to build a deck?
Almost always yes for attached decks. Most jurisdictions require a building permit for decks attached to the house, over 30" above grade, or larger than 200 sq ft. Freestanding ground-level decks under 200 sq ft may be exempt — check your local building department.
How deep should deck footings be?
Below the local frost line — typically 36-48" in northern states, 12-18" in southern states. Standard footing size is 12" diameter for residential decks. Use precast concrete pier blocks only for freestanding ground-level decks, not elevated or attached decks.
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