Deck board and screw calculator
- – rows of boards across the width
- – joists, – sq ft of deck
Put in the deck size and you get a board count you can hand to the yard, plus how many face screws or hidden clips to grab. Length is the direction the boards run. On most attached decks that's along the house.
What I'd have on hand
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How the math works
Rows are the deck width divided by one board plus one gap. Each row needs enough boards to cover the length, and the waste allowance covers butt joints, bad boards and picture-frame cuts. Fasteners assume two screws per board at every joist, or one hidden clip per board per joist, plus 5% for drops.
Diagonal decks and picture-framed borders eat more material. Bump the waste to 15% or more for those.
Common questions
How many screws per deck board?
Two face screws at every joist the board crosses. A 16 ft board on 16″ joists crosses 13 joists, so it takes about 26 screws.
What gap should deck boards have?
Most composite brands call for about 3/16″ side to side. Wet pressure-treated boards are often butted tight because they shrink as they dry. Always check the board maker's install guide.
Do composite boards need 12″ joist spacing?
Many composite and PVC boards allow 16″ on center for straight runs and require 12″ for diagonal layouts or stairs. The manufacturer's spec decides, and it affects your warranty.