Deck Materials List: How Many Boards, Joists and Screws?
A 16 × 12 ft deck with 5.5 inch boards needs about 29 deck boards (16 ft long, including 10% extra), 13 joists at 16 inches on center, and around 700 deck screws. Here's how each number is worked out, and what else goes on the list. The deck calculator handles the decking and joists for any size.
How a deck goes together
From the ground up: concrete footings, posts, beams, joists, then deck boards. Joists usually run out from the house, and deck boards run across the joists, parallel to the house.
Deck boards
rows = deck width (in) ÷ (board width + gap)
boards = rows × boards per row
For a deck that's 12 ft out from the house: 144 inches ÷ (5.5 + 0.125) = 25.6, so 26 rows. Running 16 ft boards along a 16 ft deck means one board per row: 26 boards, or 29 with 10% extra for splits, warping and end trimming.
Tip: if your deck length isn't a standard board length, buy longer boards and stagger the butt joints over joists, rather than piecing together short offcuts.
Joists
joists = deck length (in) ÷ spacing + 1
At 16 inches on center along 16 ft: 192 ÷ 16 = 12, plus 1 = 13 joists, each 12 ft long. Add two rim joists (the boards that cap the joist ends) and a ledger board if the deck attaches to the house.
Joist size depends on the span. In common US span tables, 2 × 8 joists at 16 inches on center span roughly 12–13 ft in southern pine; 2 × 10s go further. Always check your local code's span tables.
Beams, posts and footings
- Beams support the joists, usually built from two or three 2 × 8s, 2 × 10s or 2 × 12s nailed together.
- Posts (4 × 4 or 6 × 6; many codes now require 6 × 6) are typically no more than 6–8 ft apart along the beam.
- Footings go below the frost line. Use the concrete calculator in Round column mode for each footing.
Fasteners and hardware
- Deck screws: two at every joist on every board. 26 rows × 13 joists × 2 = 676, so buy about 700.
- Joist hangers: two per joist where joists meet a ledger or rim (one at each end if both ends hang).
- Ledger fasteners: structural screws or bolts at the spacing your code requires, plus flashing above the ledger.
- Post bases and beam connectors rated for exterior use.
Board spacing
- Wet pressure-treated: install tight or with a nail-width gap; it shrinks as it dries.
- Kiln-dried wood: about 1/8 inch.
- Composite and PVC: follow the manufacturer's spacing, often 3/16 inch, and their joist spacing, often 12–16 inches.
Decks are structures people stand on, so check whether you need a permit and an inspection before you start.