Deck Calculator

With standard 5.5 in boards and a 1/8 in gap you need 26 rows running the 16 ft length. Buy 16 ft boards and that is 26 boards to cover it, or 29 boards once you add a 10% waste allowance. The deck is 192 sq ft and the decking itself is 416 linear feet of board.

Buy 12 ft boards instead and the math changes badly: every row needs two boards, so 52 boards, 624 linear feet purchased for 416 feet of deck. Always check the board length comparison table above before you load the cart.

16 in on center is the default for pressure treated 5/4 and 2x decking and for most composite brands laid straight. 12 in on center is required for diagonal decking on nearly every composite, because a 45 degree board spans 1.41 times the joist spacing, and it is also common under decking laid over a stair landing.

24 in on center only works with full 2x decking, and even then it feels bouncy and most composite manufacturers void the warranty. Check the specific product's installation sheet, since the spacing rule comes from the decking manufacturer, not from the joist span table.

Below the frost line, and the frost line is set by your local building department. It ranges from essentially zero in southern Florida and coastal California to 42 in or more across Minnesota, North Dakota and northern Maine, with 36 in common across the northern half of the country and 12 to 24 in usual through the south.

Do not guess. Call the building department or check your county's adopted code amendments, because if the footing is shallow the deck will heave, pull on the ledger and rack the railing. A freestanding deck on a shallow pad forgives frost heave far better than an attached one does.

Two screws at every joist crossing. For a 16 ft board over joists at 16 in on center that is 13 crossings and 26 screws per board. Across a whole deck it works out to roughly 350 screws per 100 sq ft, which is where the rule of thumb comes from, and this calculator shows the exact number for your geometry alongside it.

Hidden fasteners are counted differently. One clip goes in the groove at every joist, so the clip count is close to board rows multiplied by joists, and you still face-screw the first and last board plus anywhere a board butts. Buy the fascia screws separately in a color-matched head.

Yes, and here is the distinction this calculator makes that most do not. The offcut column in the board length table is material you pay for and cut off because the stock length does not divide into your deck. That is geometry and it is predictable. The waste allowance on top of it covers the unpredictable part: a board with a bad crook, a split end, a miscut, a stair tread you have to redo.

Offcuts from the length mismatch are usually too short to be useful in a field of full-length rows, but they are perfect for stair treads, the fascia, and blocking. Keep them and buy the 10% anyway.

The ledger is counted in the framing linear feet when you set the deck as attached to the house. Flashing, ledger bolts, joist hangers, post bases and post caps are not counted, because the quantity depends on the specific hardware system you choose and the fastener schedule that comes with it.

As a planning figure: one joist hanger per joist end that lands on the ledger or a beam face, one post base and one post cap per post, and a structural screw or through-bolt roughly every 16 in along the ledger in a staggered pattern. The exact ledger fastener spacing is in the manufacturer's table and depends on joist span and species, so pull that table rather than using a rule of thumb.