How much lumber for a 12×20 ft deck?
Answer
58 boards, 16 joists, 10 posts
Deck area: 240 sq ftDecking boards (5.5" wide, 12' long): 58 boardsJoists (16" on center): 16Posts: 10 (2 beams)Screws: 916Linear feet of decking: 572 ftIncludes 10% waste factor
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How We Calculated This
Boards = ceil(rows × boardsPerRow × 1.10), Joists = ceil(width×12 / spacing) + 1
Area = 12 × 20 = 240 sq ft. Boards = 58 (with 10% waste). Joists = ceil(20×12 / 16) + 1 = 16. Posts = 10.
Related Calculations
How much lumber for a 8×10 ft deck?20 boards, 9 joists, 6 postsHow much lumber for a 8×12 ft deck?20 boards, 10 joists, 6 postsHow much lumber for a 10×10 ft deck?25 boards, 9 joists, 6 postsHow much lumber for a 10×12 ft deck?25 boards, 10 joists, 6 postsHow much lumber for a 10×14 ft deck?49 boards, 12 joists, 8 posts
Calculated using verified formulas. Last updated March 2026.