Deck Calculator
Estimate decking boards, joists and screws for a rectangular deck — with the waste factor real builds require.
Deck boards needed (with 10% waste)
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Deck area —
Joists —
Screws (approx.) —
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How it works
Boards = deck width ÷ (board width + gap) × waste; joists = length ÷ spacing + 1Frequently Asked Questions
How many deck boards do I need?
Divide the deck width by the board coverage (board width + gap): a 12 ft wide deck with 5.5 in boards and ¼ in gaps needs about 25 rows; multiply rows by deck length ÷ board length for the count, plus 10% waste for cuts.
How far apart should deck joists be?
16 inches on-center is standard for wood decking laid perpendicular; composite boards often require 12 in. Wider spacing causes bounce and voids most warranties.
How many screws per deck board?
Two per joist crossing — roughly 350 screws per 100 sq ft at 16 in spacing. The calculator totals it for you.