Deck Board Calculator
Estimate deck boards and lineal feet for a deck.
Length the boards run along.
Width the rows span across.
Spacing for drainage and expansion.
Results update as you type.
How it works
A deck board calculator estimates how many boards and how much total lineal footage you need to surface a deck, accounting for the small gap left between boards for drainage and expansion. You enter the deck's length and width, the width and length of the boards you will use, and the gap between them. The tool adds the gap to each board's width to find the effective space one board occupies, divides the deck width by that figure to count the rows needed across the deck, then works out how many boards make up each row along the length, and multiplies the two. That gap matters more than it seems: decking must be spaced so water drains through and the boards can swell and shrink with weather without buckling, and even an eighth of an inch across many rows changes the board count. Rounding up at each step reflects that you buy whole boards and a partial row still needs a full board. This is a planning estimate for a simple rectangular deck laid in straight rows; picture-frame borders, diagonal patterns and stairs use more, so add a waste margin of around 10 percent on top. Deck builders, carpenters and homeowners use it to price decking and order lumber. The row-and-length method is standard practice because a deck surface is simply parallel rows of boards covering a rectangle.
Row width = (board width + gap) ÷ 12; rows = ⌈deck width ÷ row width⌉; boards per row = ⌈deck length ÷ board length⌉; boards = rows × boards per row
Each board plus its drainage gap occupies an effective width, converted from inches to feet by dividing by 12. Dividing the deck width by that effective width and rounding up gives the number of rows needed to span the deck, since a partial row still requires a full board. Boards run the length of the deck, so dividing the deck length by the stock board length and rounding up gives how many boards make up one row end to end. Multiplying rows by boards per row gives the total boards, and multiplying rows by the deck length gives the total lineal feet of decking to order.
Source:Standard construction estimation (area/coverage method)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter deck length and deck width.
- 2
Adjust the options
Adjust board width, board length and gap between boards if they apply — sensible defaults are already set.
- 3
Read your result
Boards to buy updates instantly as you type — no button to press.
Frequently asked questions
How much gap should I leave between deck boards?
An eighth of an inch, or about 3 to 6 millimeters, is typical for most decking, allowing rainwater to drain through and the boards to expand and contract with temperature and moisture. Some composite products and installation systems specify their own gap, so check the manufacturer's guidance. Wet or freshly treated wood shrinks as it dries, so it can be laid tighter, while dry boards need the full gap to avoid buckling later.
How many deck boards do I need?
It depends on the deck size, the board width and the gap between boards. The calculator counts the rows needed to span the deck width, works out how many boards make up each row along the length, and multiplies them. As a rough check, a wider board covers more per row so you need fewer, while a larger gap slightly increases the row count. Always add a waste margin for cuts and pattern work on top.
Should I add extra for waste?
Yes. This estimate assumes simple straight rows, but real decks lose material to end cuts, a picture-frame border, stairs, and the occasional warped or split board rejected on site. Adding around 10 percent, and more for diagonal or herringbone layouts, covers those losses. Ordering a few spare boards also lets you replace a damaged plank years later with lumber that has weathered alongside the rest of the deck.
What is lineal feet in decking?
Lineal feet, or linear feet, is the total end-to-end length of board you need, measured along the boards regardless of their width. Lumber yards often price and sell decking by the lineal foot, so this figure lets you order and budget directly. It is the number of rows multiplied by the deck length. Note that lineal feet differs from square feet, which measures the surface area the boards cover.
Does board direction change the count?
It can. This calculator assumes boards run along the deck length with rows stacked across the width. Running the boards the other way, or on a diagonal, changes how many rows there are and how much each row must be pieced together, which affects both the board count and the waste. Diagonal layouts in particular use noticeably more material because of the angled cuts, so add extra margin when planning one.