Deck Calculator: Boards, Joists and Screws
Plan a deck build fast. Enter the deck length and width, then set your board size, the gap between boards and the joist spacing to get boards, joists and screws.
How to estimate decking materials
- Enter the deck length and width in feet.
- Set the board width, board length, gap, joist spacing and waste.
- Read off the deck boards, joists and screws to buy.
Examples
16 by 12 ft deck, 5.5 in boards, 1/8 in gap, 16 in joists
L 16, W 12, board 5.5 in x 8 ft, gap 0.125, joists 16 in, 10% waste
192 sq ft, 57 boards, 10 joists, 1140 screws
Frequently asked questions
What gap should I leave between deck boards?
About 1/8 inch (0.125 in) is common for kiln dried lumber that has already shrunk, while wet treated boards can be butted tight since they shrink as they dry. The default gap is 1/8 inch.
How far apart should deck joists be?
Sixteen inches on center suits most residential decks and composite boards. Twelve inches adds stiffness for diagonal patterns or thinner boards. The calculator defaults to sixteen inches.
How many screws does a deck need?
Plan on two screws where each board crosses each joist. The estimate multiplies boards by joists by two, so a longer board over more joists uses more fasteners, just as it does on site.
How much waste should I add for decking?
Around 10 percent covers saw cuts, board ends and the occasional cull. Diagonal or herringbone layouts waste more off each cut, so raise the percentage for angled designs.
Do board length and width change the board count?
Yes. Each board covers its width plus the gap, times its length. Wider or longer boards cover more area, so the calculator needs fewer of them to fill the same deck.
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