12 × 20 deck cost & materials
Short answer
A 12 × 20 ft deck is 240 square feet. In composite it costs about $7,200–$14,400 installed and needs roughly 36 deck boards and 16 joists.
Area
240 sq ft
Composite cost
$7,200–$14,400
Deck boards
36
Joists
16
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Frequently asked questions
How many deck boards for a 12 × 20 deck?
About 36 16-ft boards (5½" wide) for 240 sq ft, including 10% waste. Longer boards mean fewer pieces but more offcuts.
How much does a 12 × 20 deck cost?
A composite 12 × 20 deck costs about $7,200–$14,400 installed. Pressure-treated wood is cheaper; PVC costs more.
How many joists for a 12 × 20 deck?
About 16 joists at 16" on center, plus 8 footings. Enter your exact size and spacing in the calculator.