Deck board calculator
Enter the deck's size and the boards you are using. You get the number of boards to buy, the linear feet, and the fasteners for every joist crossing.
Inputs
Result
How it is worked out
A 16 by 12 ft deck in 5-1/2 in boards with a 3/16 in gap is 26 rows. That is 416 linear feet, 29 boards of 16 ft with 10% waste, and 338 joist crossings: 676 screws or 338 clips.
Picking a board length
A board long enough to span the deck in one piece saves time and looks better. Where it cannot, stagger the butt joints so no two are on the same joist in neighbouring rows, and land every joint on a joist, doubled or with a block if your board maker asks for it.
Diagonal boards look good and stiffen the frame, but they cut more and need closer joists. Plan on 12 in spacing for 45° decking unless the board's maker says otherwise.
Questions
How many deck boards do I need?
Divide the deck's width in inches by the board width plus the gap to get the rows, multiply by the deck's length for linear feet, add waste and divide by the board length. A 16 x 12 ft deck in 5-1/2 in boards takes 29 sixteen-footers.
How many screws per deck board?
Two at every joist. A 16 ft board on joists at 16 in crosses 13 joists, so 26 screws. A 16 x 12 ft deck takes about 680.
What gap should deck boards have?
About 3/16 in for dry wood and many composites. Wet pressure-treated boards shrink as they dry, so they are often laid tight. Composite makers specify the gap on the box.
How much extra decking should I buy?
10% for straight runs, 15% or more for diagonal or picture-frame borders.
How far apart should deck joists be?
16 in on centre for most straight decking, 12 in for diagonal boards and for many composites. The board maker's span limit governs.
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