How to Calculate Deck Materials
Boards: Deck area ÷ (board width + gap) ÷ board length. Standard 5/4×6 decking is actually 5.5 inches wide.
Related: Try our fence calculator, lumber calculator, or stair calculator for your project.
Joists: With boards running the deck length, joists = ceil(deck length ÷ joist spacing) + 1. Rotate the orientation if your framing plan differs. Use 2×8 or 2×10 lumber for 16" spacing.
Screws: ~350 screws per 100 sq ft (2 screws per joist per board).
Cost Comparison
| Material | $/sq ft | 12×16 Deck | Maintenance |
|---|
| Pressure-treated | $2-3 | $400-600 | Annual seal |
| Cedar | $3-5 | $600-1000 | Every 2-3 yrs |
| Composite | $4-8 | $800-1600 | None |
How to Plan and Build a Deck
A deck is one of the highest-ROI home improvements, returning 60–80% of cost at resale. But a safe, long-lasting deck requires careful planning before you buy a single board. Follow this sequence to avoid costly rework.
- Check local codes and permits. Most jurisdictions require a permit for decks over 12–30 inches above grade. Setback requirements, railing height (36" or 42"), and post spacing vary by location. Pull the permit before you dig.
- Determine size and shape. A 12×16 ft deck (192 sq ft) is the most popular size for outdoor dining and seating. Allow at least 36" of clearance around furniture. Use our square footage calculator to compare layouts.
- Plan the foundation. Decks need concrete footings below the frost line (typically 36–48" deep). Use 6×6 posts anchored to footings with galvanized post bases. Space footings according to your beam span — usually 6–8 feet apart.
- Frame the structure. Install a ledger board against the house (with proper flashing), set support posts, then install beams and joists. Joists are typically 2×8 or 2×10 at 16" on center. Use 12" spacing for composite decking or heavy loads.
- Lay the decking. Start at the house and work outward. Leave a 1/8" gap between boards (1/4" for wet wood). Use hidden fasteners or color-matched deck screws. Stagger butt joints for strength and appearance.
- Add railings and stairs. Railings are required for decks over 30" high. Balusters must be spaced so a 4" sphere cannot pass through. Stairs need a 36" minimum width and graspable handrails on both sides if over 30" high.
Deck Materials: A Complete Comparison
| Material | $/sq ft (material) | Lifespan | Maintenance | Best For |
|---|
| Pressure-treated pine | $2–$3 | 10–15 yrs | Annual seal/stain | Budget decks, framing |
| Cedar | $3–$5 | 15–20 yrs | Every 2–3 yrs | Natural look, insect resistance |
| Redwood | $4–$7 | 15–25 yrs | Every 2–3 yrs | Premium natural appearance |
| Composite (WPC) | $4–$8 | 25–30 yrs | Annual soap wash | Low-maintenance, no splinters |
| PVC / vinyl | $5–$10 | 25–30 yrs | None | Maximum durability, no wood content |
| Aluminum | $8–$15 | 30+ yrs | None | Commercial, waterfront, fire-prone areas |
Composite decking is the fastest-growing segment because it eliminates annual staining and resists rot and insects. However, it can scratch more easily than wood and may fade slightly in direct sun over 10+ years. Premium capped composites (with a protective shell on three or four sides) resist fading and staining best.
Material Quantities by Deck Size
| Deck Size | Sq Ft | Deck Boards (16 ft) | Joists (2×8) | Screws (approx) | Concrete Footings |
|---|
| 10 × 12 | 120 | ~18 | ~10 | ~420 | 4–6 |
| 12 × 12 | 144 | ~21 | ~10 | ~500 | 4–6 |
| 12 × 16 | 192 | ~28 | ~13 | ~670 | 6–8 |
| 16 × 16 | 256 | ~37 | ~13 | ~900 | 6–9 |
| 16 × 20 | 320 | ~47 | ~16 | ~1,120 | 8–10 |
Quantities assume 5/4×6 decking at 16" joist spacing with 10% waste. Use our lumber calculator for precise board-foot calculations on framing members.
Deck Stairs: Calculation and Code
Deck stairs are often the most complex part of a project. The golden rule is uniformity: every step must have the same rise (vertical) and run (horizontal) to prevent tripping.
- Rise: Maximum 7.75" per step (IRC code). Measure total height from deck surface to ground, divide by 7.75, round up to get number of steps, then divide total height by step count for exact rise.
- Run: Minimum 10" tread depth. 11–12" is more comfortable. Use 2×12 stringers cut with a framing square.
- Stringers: Space 16" apart. A 36" wide stair needs 3 stringers. Use 2×12 lumber; never notch more than the maximum allowed (typically 6.5" from the back of a 2×12).
- Landing: Required at the bottom (minimum 3×3 ft) and at the top (the deck surface counts).
Our stair calculator computes rise, run, stringer length, and angle automatically.
Total Cost Breakdown
Material is only part of the budget. Here is what a typical 12×16 deck actually costs:
| Component | Wood Deck | Composite Deck |
|---|
| Decking boards | $400–$600 | $800–$1,600 |
| Framing (joists, beams, posts) | $300–$500 | $300–$500 |
| Concrete footings | $100–$200 | $100–$200 |
| Hardware (screws, brackets, flashing) | $150–$250 | $200–$400 |
| Railings | $200–$500 | $400–$1,000 |
| Stairs (if needed) | $100–$200 | $150–$300 |
| Total materials | $1,250–$2,250 | $1,950–$4,000 |
| Professional labor | $1,500–$3,000 | $2,000–$4,000 |
Common Deck Building Mistakes
- Undersized footings. Footings must extend below the frost line. Shallow footings heave in winter, causing cracks and structural failure.
- Missing ledger flashing. Water intrusion behind the ledger board is the #1 cause of deck failure. Use proper Z-flashing or a membrane between ledger and house.
- Too-wide joist spacing. 16" on center is standard for wood decking. Composite often requires 12" or 16" — check the manufacturer spec.
- Not using corrosion-resistant fasteners. Regular screws rust and stain the deck. Use stainless steel or ceramic-coated deck screws, especially with ACQ-treated lumber.
- Ignoring railing code. Railings must be 36" (or 42" in some areas) with balusters spaced ≤4". A 4" sphere test is the standard.
- Building without a permit. Unpermitted decks can fail home inspections and reduce resale value. The permit fee is small compared to the risk.
FAQ
How much for a 12×16 deck?
Materials: $3,000-8,000. Wood ~$3,000, composite ~$6,000-8,000. Labor adds $1,500-3,000.
How many deck boards?
A 12×16 deck with 16ft 5/4×6 boards needs ~28 boards (with 10% waste).
Joist spacing?
16 inches on center standard. 12 inches for heavy loads or diagonal patterns.
Wood or composite?
Wood is cheaper but needs annual maintenance. Composite costs 2x more but lasts 25+ years with no upkeep.