Deck Board Calculator
Type in your deck size, the board width and the gap you want between boards, and see how many boards to buy - by length, with waste built in. It also works out the joists and the screws or hidden clips you need, plus the cost. Works in feet/inches or metric, updates as you type. Nothing uploaded.
Results
Deck Plan
Board run direction shown to scale
Boards by Stock Length
| Stock length | Boards needed | Total length |
|---|
Cost Estimate
Enter a price per board to see cost. Boards only - joists, fasteners and footings are not included.
Learn more: deck board estimating
How board count is worked out
Decking runs in courses (rows) laid side by side. The number of courses is set by the deck dimension running across the boards, divided by the board width plus the gap. Take a 16 ft by 12 ft deck with boards running along the 16 ft length: the courses stack across the 12 ft (144 in) width. With 5.5 in boards and a 0.25 in gap each course takes up 5.75 in, so you need ceil(144 / 5.75) = 26 courses. Each course is 16 ft long, giving 26 x 16 = 416 linear feet of decking before waste.
Stock lengths, waste and cost
Lumber is sold in fixed lengths (8, 10, 12 and 16 ft, or 2.4-4.8 m). To turn linear feet into boards to buy, the calculator applies a waste multiplier and divides by your chosen stock length. For the 416 ft example with a 16 ft stock length and 10 percent waste, that is ceil(416 x 1.10 / 16) = 29 boards. A diagonal layout adds about 15 percent on top, since angled cuts leave large offcuts; a picture-frame border adds about 10 percent. Multiply boards by your price per board for a material estimate.
Joists and fasteners
Boards always sit across the joists, so the joists run the other way to the decking. Joist count is the board run length divided by the on-center spacing, plus one for the closing joist: a 16 ft run at 16 in centers needs floor(16 ft / 16 in) + 1 = 13 joists. Fasteners are counted where each board crosses each joist. Face screws use two per crossing (26 courses x 13 joists x 2 = 676 screws); hidden clips use one per crossing (338 clips), giving a fastener-free top surface.
FAQ
How many deck boards do I need?
Divide the deck dimension running across the boards by the board width plus the gap, then round up. For a 12 ft wide deck with 5.5 in boards and a 0.25 in gap, the pitch is 5.75 in, so you need ceil(144 / 5.75) = 26 board courses. Multiply by the board run length and divide by your stock length to get the number of boards to buy.
How much waste should I add for a diagonal or picture-frame deck?
A straight layout wastes very little, so 5-10 percent covers offcuts. A 45-degree diagonal layout creates large triangular offcuts at every board end, so this calculator adds about 15 percent on top of your own waste figure. A picture-frame border with mitred corners adds roughly 10 percent. You can still adjust the extra waste slider for your own conditions.
How many screws or hidden clips does a deck need?
Fasteners are counted at every point a board crosses a joist. With face screws you use two per board per joist, so a deck of 26 board courses over 9 joists needs 26 x 9 x 2 = 468 screws. Hidden clip systems use one clip per crossing instead, so the same deck needs 234 clips plus a few starter clips at the edges.