How to Calculate Deck
What is Deck?
A deck calculator estimates the lumber, hardware, and materials needed to build a wooden deck. It accounts for deck dimensions, board spacing, joist layout, and waste to generate a cut list and material order.
Formula
Decking boards = (deck area ÷ board coverage per piece) × (1 + waste %)
Step-by-Step Guide
- 1Calculate deck surface area (length × width)
- 2Determine coverage per board based on board width minus gap spacing
- 3Apply 10–15% waste factor for cuts and defects
- 4Separately calculate joists, posts, beams, and fasteners
Worked Examples
Input
16 ft × 20 ft deck · 5/4×6 boards (5.5 in wide) · 1/4 in gap
Result
≈ 69 boards needed at 10% waste on 320 sq ft deck
Use treated lumber rated for ground or above-ground contact as appropriate
Common Mistakes to Avoid
- ✕Forgetting to add waste factor for angled or diagonal patterns
- ✕Not accounting for joist spacing in deck board count
Ready to calculate? Try the free Deck Calculator
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