20 × 20 deck cost & materials
Short answer
A 20 × 20 ft deck is 400 square feet. In composite it costs about $12,000–$24,000 installed and needs roughly 61 deck boards and 16 joists.
Area
400 sq ft
Composite cost
$12,000–$24,000
Deck boards
61
Joists
16
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Frequently asked questions
How many deck boards for a 20 × 20 deck?
About 61 16-ft boards (5½" wide) for 400 sq ft, including 10% waste. Longer boards mean fewer pieces but more offcuts.
How much does a 20 × 20 deck cost?
A composite 20 × 20 deck costs about $12,000–$24,000 installed. Pressure-treated wood is cheaper; PVC costs more.
How many joists for a 20 × 20 deck?
About 16 joists at 16" on center, plus 8 footings. Enter your exact size and spacing in the calculator.