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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