Deck Boards Calculator (Boards, Joists and Screws)
Enter the deck size, board size and joist spacing.
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Deck Boards Calculator (Boards, Joists and Screws) by TheCalcTools
How the Deck Boards Calculator (Boards, Joists and Screws) works
Rows of boards = deck width ÷ (board width + gap). Each row needs deck length ÷ board length boards. Joists sit every 16 inches (12 for diagonal boards or some composites), with two screws per board at each joist.
Composite decking often needs specific gaps and joist spacing; follow the manufacturer’s guide.
The formula
Worked example
Using the default values shown in the calculator:
| Deck width across the boards (ft) | 12 |
|---|---|
| Deck length along the boards (ft) | 16 |
| Board width (in) | 5.5 |
| Gap between boards (in) | 0.1875 |
| Board length (ft) | 16 |
| Joist spacing (in) | 16 |
| Waste | 10 % |
- A 12 × 16 ft deck with 5.5 in boards and 3/16 in gaps: 26 rows, 29 boards of 16 ft with waste.
- About 520 screws.
Result:
| Deck boards | 29 |
|---|---|
| Linear feet of decking | 416 |
| Joists (spanning the length) | 10 |
| Screws (2 per board per joist) | 520 |
| Rows of boards | 26 |
Frequently asked questions
What gap between deck boards?
About 3/16 inch for kiln-dried or composite boards; wet pressure-treated boards can be laid tight because they shrink.
Sources and further reading
- American Wood Council: Prescriptive residential wood deck construction guide (DCA 6)
- Wikipedia: Deck (building)
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.