Use two deck screws at every point where a board crosses a joist. Across a whole deck, that works out to about 350 screws per 100 square feet. From there it's just a matter of counting joist crossings, which is easy once you know your joist spacing.
For a solid box-count estimate on your specific deck, the deck board calculator figures fasteners along with board quantity.
The two-screw rule
Each deck board should get two screws wherever it passes over a joist. Two fasteners per crossing keep the board from cupping, twisting, or working loose as it expands and contracts through the seasons. One screw lets a board pivot and lift; two lock it flat.
Drive each screw about 3/4 inch in from the board's edge so you bite solid wood without splitting it, and sink the head flush or just below the surface. An impact driver makes consistent, clean driving far easier than a drill, especially across hundreds of screws.
Counting joist crossings
The number of screws per board comes straight from how many joists it crosses. Joist spacing is usually:
- 16 inches on center for most decks
- 12 inches on center for composite decking or diagonal board layouts, which need closer support
At 16-inch spacing, a board crosses a joist roughly every 16 inches along its length. A 16-foot board crosses about 12 joists, so:
- Joists crossed: about 12
- Screws per crossing: 2
- Screws per board: about 24
Tighten the joists to 12 inches on center and that same board crosses more joists, pushing the per-board count higher. That's the trade-off with composite and diagonal designs: more support points mean more fasteners.
The 350-per-100-square-feet shortcut
For ordering, skip the per-board count and use the rule of thumb: about 350 deck screws per 100 square feet of deck surface. That figure already bakes in two screws per joist crossing at typical spacing, so you can buy by the box without counting every board.
To estimate your order:
- Find your deck area in square feet.
- Divide by 100.
- Multiply by 350.
A 300-square-foot deck, for example, needs roughly 1,050 screws. Buy a little extra, because some will strip, snap, or miss the joist and need replacing.
Tight on joists at 12 inches on center? Nudge your estimate upward, since closer joists mean more crossings and more screws.
Screws, or hidden fasteners?
Face-screwing is the traditional method: fast, strong, and cheap, with visible screw heads in neat rows. If you want a clean surface with no visible fasteners, hidden deck fasteners clip into a groove milled in the board edge instead. The look is cleaner, but the system costs more and changes your fastener count, so check the clip manufacturer's coverage rather than the 350 rule. Many composite decks are built this way.
Pick the right screw
Quantity is only half the job; the screw itself matters.
- Material. Use coated, stainless, or composite-rated screws that resist corrosion. Cheap interior screws rust and stain the wood around them.
- Length. The screw should penetrate the joist by at least 1 inch beyond the board thickness for a solid grip.
- Type. Composite-specific screws have reverse threads or a head designed to sit flush without mushrooming the board surface.
Driving consistently matters too. Hold your fastener straight so you don't shift the board and ruin the spacing you set; our guide on how to space deck boards covers keeping those gaps even as you fasten.
The bottom line
Two screws at every joist crossing is the rule, which lands at about 350 screws per 100 square feet at standard 16-inch joist spacing. Bump that up for 12-inch spacing, composite, or diagonal layouts, and switch to a clip-coverage estimate if you go hidden-fastener. Run your real dimensions through the deck board calculator and you'll have a solid estimate of how many boards, and how many screws, to bring home.