How many deck boards do I need? Boards, gaps and screws
Divide the deck’s width across the boards by the board face plus its gap to get the rows, multiply by the boards each row needs and add 10% extra. A 5.5-inch board with a 1/8-inch gap covers 5.625 inches.
A 16 × 12 ft deck with 16 ft boards running along it has 26 rows of one board each. With 10% extra that is 29 boards.
Worked example
Example: a 16 × 12 ft deck, boards along the length, 5.5-inch faces, 1/8-inch gaps, 16 ft boards and 10% extra.
This example gives 29 deck surface boards.
- ceil((12 + 0.010417) ÷ (0.458333 + 0.010417)) = 26
- ceil(26 × 1 × (1 + 10/100)) = 29
Other calculators for this job
Every step of a deck project: measure, the list, what it costs and the quotes.
What changes the order?
Turning the boards changes the number of rows and the boards each row needs, though the deck area stays the same.
| Calculator input | Result from those inputs |
|---|---|
| Boards run along: length | 29 deck surface boards |
| Boards run along: width | 39 deck surface boards |
Try your own measurements in the deck board calculator.
New deck or new boards?
Replacing boards on sound framing is a surface job; a new deck adds framing, footings, stairs and railing. Know which one you are pricing before you count.
Use the real board size
A 5/4 × 6 deck board and a 2 × 6 are both about 5.5 inches wide. Add the gap the board maker asks for: about 1/8 inch is common for wood, and composite makers print their own.
Lengths and seams
Pick a stock length that covers the deck in one piece if you can, such as 16 ft boards on a 16 ft deck. Where boards meet end to end, each seam needs a joist under it, and staggered seams look better. The calculator does not reuse offcuts.
Screws and the rest
Boards take two screws at every joist: on joists 16 inches apart a 16 ft board crosses 13 joists, so 26 screws. Joists, beams, posts and footings come from your plan or local code; the framing calculator counts them from the plan.