Decking Calculator

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.

Board count formula (area method): Coverage per board = Board Length × Board Width Boards needed = (Deck Area ÷ Coverage per board) × Waste Factor

Round up to the nearest whole board. This calculator uses the full board width for a fast estimate. For a gap-precise count that subtracts the expansion gap, use the Deck Board Spacing calculator.

Linear footage: Total Linear Footage = Boards Needed × Board Length Multiply that by your local price per linear foot to estimate material cost. Add 10–15% waste for cuts and damaged boards, 15–20% for diagonal layouts.

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 × 20 ft = 320 sq ft. Using 5/4 × 6 boards (5.5 in wide) in 20-ft lengths, 15% waste.

Coverage per board = 20 × (5.5 ÷ 12) = 9.17 sq ft Boards needed = (320 ÷ 9.17) × 1.15 = 34.9 × 1.15 = 40.1 → 41 boards Total linear footage = 41 × 20 = 820 linear ft At $5.50 per linear foot, materials run about 820 × $5.50 = $4,510. The calculator returns the board count and linear feet; multiply by your own price for the cost.