Decking Calculator
Calculate how many deck boards you need for your project.
Enter deck dimensions and board size to estimate materials and cost.
Deck board quantity and cost calculation determines the number of deck boards needed to cover a given surface area, accounting for board dimensions, gaps between boards, and waste from cuts.
Net board coverage formula: Effective Board Width = Actual Board Width − Gap Width
Boards needed (parallel to deck length): Number of Boards = Deck Width (inches) ÷ Effective Board Width
Round up to the nearest whole number.
Linear footage per board: Total Linear Footage = Number of Boards × Deck Length (feet)
Board count: Board Count = Total Linear Footage ÷ Board Length Add 10–15% waste factor for cuts and damaged boards.
Cost formula: Material Cost = Total Linear Footage × Cost per Linear Foot Total Project Cost = Material Cost + Fastener Cost + Labor Cost
Standard deck board dimensions:
- Nominal 5/4 × 6: actual 1 inch × 5.5 inches — most common composite and pressure-treated decking
- Nominal 2 × 6: actual 1.5 inches × 5.5 inches — heavier option; also used for framing
- Standard board lengths: 8, 10, 12, 16, 20 feet
Standard gap spacing:
- Pressure-treated wood: 1/4 inch gap (wood swells when wet)
- Composite decking (Trex, TimberTech): 1/8–3/16 inch (per manufacturer)
- Hidden fastener systems: gap determined by fastener clip width
Decking material costs (2024 US, per linear foot):
- Pressure-treated pine (5/4 × 6): $1.50–$3.00
- Cedar (5/4 × 6): $3.00–$6.00
- Redwood: $5.00–$10.00
- Composite (Trex, mid-grade): $4.00–$8.00
- PVC/composite (high-end): $7.00–$15.00
What each variable means:
- Actual vs nominal width — lumber is sold by nominal dimensions but milled smaller; always use actual measurements for calculations
- Gap allowance — gaps allow drainage and prevent moisture-trapping rot; also accommodate thermal expansion of composite boards
- Waste factor — end cuts, angle cuts for diagonal decking, and damaged boards typically account for 10–15%; go to 15–20% for diagonal or picture-frame layouts
Worked example: Deck: 16 ft wide × 20 ft long. Using 5/4 × 6 composite (actual 5.5 in wide). Gap: 3/16 in.
Effective board width = 5.5 − 0.1875 = 5.3125 inches Boards across = (16 × 12) ÷ 5.3125 = 192 ÷ 5.3125 = 36.1 → 37 boards Total linear footage = 37 × 20 ft = 740 linear ft + 12% waste = 829 linear ft Cost at $5.50/lin ft = $4,560 in materials. Labor (150 sq ft/day, 2 workers) ≈ $1,800. Total ≈ $6,360.