Decking Calculator

Calculate deck area (length × width), then divide by coverage per board (board length × board width). A 12 ft × 5.5" board covers 5.5 sq ft. Add 10-15% for waste from cuts, defects, and diagonal patterns. For a 16×12 ft deck (192 sq ft) with 12 ft boards: 192÷5.5=35 boards + 10% = 39 boards needed.

Standard is 16" on center for 5/4 wood decking. Composite decking often requires 12" or 16" depending on manufacturer—always check specs. Diagonal patterns need 12" spacing. Closer spacing reduces bounce and increases strength. 24" spacing is only acceptable for 2× lumber perpendicular to joists, rarely recommended for decking.

Pressure-treated pine: USA $2-4/linear ft, $8-15/sq ft installed; Canada C$3-6/ft; UK £3-8/m. Cedar: $4-8/ft. Composite: $5-15/ft, $15-30/sq ft installed. Hardwood (ipe, mahogany): $8-20/ft. Labor adds 50-100% of material cost. Total deck cost: $15-45/sq ft depending on materials and complexity.

Use 2 screws per board at each joist. With 16" joist spacing and 5.5" boards: approximately 350 screws per 100 sq ft. A 192 sq ft deck needs about 700 screws. Use stainless steel or coated deck screws to prevent corrosion. Hidden fastener systems use fewer visible screws but cost more. Buy 10% extra for mistakes.

Wood costs less upfront but needs annual maintenance (staining/sealing). Pressure-treated lasts 15-20 years; cedar 20-25 years. Composite costs 2-3× more but is virtually maintenance-free, lasting 25-50 years. Composite doesn't splinter—good for barefoot areas. Wood looks more natural. Consider lifetime cost: composite often cheaper long-term despite higher initial investment.

Divide deck length by joist spacing, then add 1. For 16 ft deck with 16" spacing: (16×12)÷16+1=13 joists. Add rim joists (2 for ends) and blocking if required by span. Standard joists are 2×8 for up to 10 ft spans, 2×10 for up to 14 ft. Always check local codes for beam and post requirements.