How the deck calculator works
Choose the board length to fit your deck
If the deck length is an exact multiple of a stock length (12, 16 or 20 ft), every row can be one board with no butt joints. When rows need two boards, stagger the joints and make sure every joint lands on a joist — many builders double the joist there.
Joist spacing
16 inches on center is standard for most wood decking laid straight. Composite boards and diagonal layouts often require 12-inch spacing — check the decking manufacturer's installation guide, since following it is usually a condition of the warranty.
Fasteners
Two screws per board at every joist is the norm for face screwing. Hidden clip systems for composite use one clip per board per joist instead. Use coated or stainless deck screws rated for treated lumber.
Frequently asked questions
How many deck boards for a 12x16 deck?
With boards running the 16 ft length, 26 rows of 5.5-inch boards are needed — 29 boards of 16 ft including 10% waste.
How many screws per deck board?
Two screws at every joist the board crosses. A 16 ft board on joists 16 inches apart crosses 13 joists, so 26 screws.
What gap should deck boards have?
About 1/8 inch for kiln-dried or composite boards; wet pressure-treated boards are often butted tight because they shrink as they dry. Follow your manufacturer.