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Deck Fastener Count Calculator

Count the screws or hidden fasteners for a deck from its size, board width and joist spacing — plus how many boxes to buy.

Deck length (along boards)

Deck width (across boards)

Board face width

Gap between boards

Joist spacing

Fasteners per board at each joist

Fasteners per box

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How it works

Boards = ⌈width ÷ (board width + gap)⌉ · Joists = ⌊length ÷ joist spacing⌋ + 1 · Fasteners = boards × joists × per-joint · Boxes = ⌈fasteners × 1.1 ÷ per-box⌉

Every deck board is fastened where it crosses each joist, so the total is the number of board rows times the number of joists times the fasteners per crossing — two screws per joist for face-screwing, or one clip per joist for hidden systems. The board rows come from the deck width divided by each board’s covered width (face plus the gap), and the joist count from the deck length divided by the on-center spacing, plus one for the starting joist. A 10% cushion covers drops, strip-outs and mistakes.

Worked example

A 16 ft × 12 ft deck with 5.5" boards and a 1/8" gap has ⌈144 ÷ 5.625⌉ = 26 board rows. At 16" joist spacing there are ⌊192 ÷ 16⌋ + 1 = 13 joists. Two screws per crossing is 26 × 13 × 2 = 676 screws; with 10% spare, buy about 744 — or 3 boxes of 350.

Frequently asked questions

How many screws per deck board?

The standard is two screws where each board crosses each joist, which resists cupping and squeaks. At 16" joist spacing a 16 ft board crosses about 13 joists, so roughly 26 screws per board; hidden-fastener systems use one clip per joist instead.

Face screws or hidden fasteners?

Face screws are cheapest and strongest and leave visible heads; hidden fasteners (clips that grip a groove in the board edge) give a clean, screw-free surface but cost more and add labor. Set the fasteners-per-joist to 2 for screws or 1 for most clip systems.

Why add 10%?

Screws strip, snap, or get dropped through the deck, and it is far cheaper to have a few left over than to stop mid-project for another box. The 10% cushion also covers stair treads, fascia and blocking you may not have counted.

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This calculator is for educational purposes. Double-check important results before acting on them.