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A deck board calculator works out how many deck boards and screws you need from the deck size, the board width and the gap you'll leave between boards. It counts boards by their actual coverage — width plus gap — so the number matches what you'll lay, not an idealised figure.
Decking spacing matters: a nominal 5.5 in board with a 1/4 in drainage gap covers 5.75 in, and that small difference adds up across a deck. This builds it in, then adds the screw count and the upgrades worth buying.
Each board covers (width + gap) × board length. Boards = deck area × waste multiplier ÷ that coverage. Linear feet = boards × board length. Screws ≈ 350 per 100 sq ft for face-screwed boards (two per joist crossing); hidden-fastener systems use clips instead. Boards run perpendicular to the joists.
A 16 × 12 ft deck (192 sq ft) with 5.5 in boards at a 1/4 in gap and 16 ft boards needs about 28 boards and ~670 screws.