Deck Board Calculator
By Taro Schenker | Updated February 11, 2026
Quick Answer: To calculate deck boards, divide your deck area (sq ft) by the coverage of one board: Board Width (in) / 12 x Board Length (ft). For standard 5.5-inch x 12-foot boards, each covers 5.5 sq ft. Board weights per linear foot: pressure-treated 2.3 lbs, cedar 1.7, composite 2.8, tropical hardwood 3.5. Plan for 3.5 screws per sq ft. Add 10% waste for rectangular decks. For a 12x16 ft deck (192 sq ft) with 5.5" x 12' boards, you need about 39 boards.
Calculate how many deck boards you need for your project. Enter your deck dimensions, choose your board size and material, and get the exact number of boards, screws, joists, total weight, and estimated cost.
How to Calculate Deck Boards
The formula for calculating the number of deck boards is:
Where Board Area = (Board Width in inches ÷ 12) × Board Length in feet.
- Measure the total deck area in square feet (length × width).
- Choose your board size — the most common is 5.5" wide × 12' long.
- Calculate the coverage area of a single board (width in feet × length).
- Divide the deck area by the single board area to get the base board count.
- Add 10% for waste from cuts, angled edges, and defective boards.
- Round up to the nearest whole board.
Deck Board Material Comparison
Compare the most popular decking materials by cost, lifespan, and maintenance:
| Material | Cost per Board | Lifespan | Maintenance |
|---|---|---|---|
| Pressure-Treated | $8 - $15 | 15 - 20 years | Stain/seal every 2-3 years |
| Cedar | $15 - $25 | 15 - 25 years | Seal every 1-2 years |
| Composite | $20 - $45 | 25 - 50 years | Occasional cleaning |
| Tropical Hardwood | $30 - $60 | 30 - 75 years | Oil annually or let patina |
Board Sizes & Coverage
Quick reference for how many boards cover 100 square feet at common sizes:
| Board Size | Area per Board | Boards per 100 sq ft |
|---|---|---|
| 3.5" × 8' | 2.33 sq ft | 43 boards |
| 5.5" × 8' | 3.67 sq ft | 28 boards |
| 5.5" × 12' | 5.50 sq ft | 19 boards |
| 5.5" × 16' | 7.33 sq ft | 14 boards |
| 7.25" × 12' | 7.25 sq ft | 14 boards |
Deck Building Tips
- Joist spacing: Standard joist spacing is 16 inches on center. For diagonal decking or composite boards, reduce to 12 inches on center for better support.
- Board direction: Run boards perpendicular to the house for the best appearance and water drainage. Plan your board length to minimize end-to-end joints.
- Acclimate boards: Let pressure-treated and cedar boards acclimate on site for 2-3 days before installation to reduce warping and shrinkage.
- Fastener choice: Use stainless steel or coated deck screws rated for your board material. Never use drywall screws — they corrode and snap.
- Waste factor: Budget 10% extra for a rectangular deck, 15% for angled or complex shapes. Longer boards reduce waste from butt joints.
- Permits: Most decks over 200 square feet or more than 30 inches off the ground require a building permit. Check your local codes before starting.
Formula Summary
Board Count Formula: To calculate the number of deck boards needed, divide the deck area by the coverage area of a single board, then multiply by the waste factor.
$$N_{\text{boards}} = \lceil \frac{A_{\text{sq ft}}}{\frac{W_{\text{in}}}{12} \times L_{\text{ft}}} \times (1 + W\%) \rceil$$
Screws: $$N_{\text{screws}} = \lceil A_{\text{sq ft}} \times 3.5 \rceil$$
Joists: $$N_{\text{joists}} = \lceil \frac{\text{Deck Width (ft)}}{16/12} \rceil + 1$$ (at 16" on-center spacing)
Weight: $$W_{\text{lbs}} = N_{\text{boards}} \times L_{\text{ft}} \times \rho_{\text{lbs/ft}}$$
| Board Material | Weight (lbs/linear ft) |
|---|---|
| Pressure-Treated | 2.3 |
| Cedar | 1.7 |
| Composite | 2.8 |
| Tropical Hardwood | 3.5 |
Standard Assumptions: Default waste factor is 10%. Screw density is 3.5 per sq ft (~350 per 100 sq ft). Joist spacing is 16 inches on center. Board widths: 3.5" (narrow), 5.5" (standard), 7.25" (wide). Board lengths: 8, 10, 12, 16, or 20 feet.
Related Calculators
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- Board Foot Calculator — measure and price lumber in board feet
- Concrete Calculator — estimate concrete for deck footings and piers
- Fence Calculator — calculate materials for fences and deck railings
Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.
Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.