Deck Board Calculator
Enter the deck's length and width, the board width and the gap you will leave, and get the boards to buy from your stock length and the screws, with the waste on the total; the working shows the rows across, the boards in each row and the joists crossed.
Estimates for planning, not professional advice. Read the full notice.
Example: a deck
29 5-4x6 board, 16 ft
- Rows of boards across the deck 26
- Boards before waste 26
- Joists the boards cross 13
- Screws, at the number you chose for each board and joist 676
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Deck boards | 5-4x6 board, 16 ft | 29 |
| Deck screws | deck screws | 676 |
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Worked example: a deck
Show the working
- Rows: the deck width plus one gap, over a board plus a gap, rounded up 12 ft + 3/16 in ÷ 5 11/16 in = 26 rows
- Boards in each row: the run over the stock length, rounded up 16 ft ÷ 16 ft = 1 board in each row
- Boards before waste 26 rows × 1 board in each row = 26 boards
- Add the waste allowance and round up once 26 boards + 10 % waste = 29 × 5-4x6 board, 16 ft
- Screws: rows times joists crossed times screws at each crossing 26 rows × 13 joists × 2 screws = 676 screws
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Waste allowance | 10% | |
| Default Your own allowance, added once to the total. Check your label or supplier. | ||
Feet and inches, like 12' 6"
This deck by stock length
Boards per row, boards before waste, joists and the stock left over, for the deck above at each stock length, cutting each row on its own and with offcuts shared
| Stock length | Boards in each row | Boards before waste | Left over from the stock | Boards if offcuts are shared |
|---|---|---|---|---|
| 8 ft | 2 | 52 | 0 in | 52 |
| 10 ft | 2 | 52 | 104 ft | 52 |
| 12 ft | 2 | 52 | 208 ft | 35 |
| 16 ft | 1 | 26 | 0 in | 26 |
| 20 ft | 1 | 26 | 104 ft | 26 |
Every figure is the deck in the example above, with each stock length in turn. The left-over column is the stock bought less the rows laid, in feet and inches; sharing offcuts cuts a row's short end from another row's board.
Questions
How many deck boards do I need for a 20x20 deck?
The calculator gives 86 boards before waste for a 20x20 deck of the board width and gap in the example, with the stock length in the example; change any of them and the count changes. The waste allowance goes on top, rounded up once.
How far apart should I space deck boards?
The gap is the number you type: the calculator does not choose it. Wood boards and composite boards are installed with different gaps, so use the figure in your board's installation guide; the rows and the boards change with it.
How many screws are there for each board?
The tool counts the screws at every place a board crosses a joist, at the number you pick for each crossing. Check the fastener count against your product's installation guide.