Deck Boards & Joists
Count decking boards, joists, and fasteners from your deck's length and width.
Estimates only — verify with local code and the product label.
How this works
This is a material count, not a structural design — joist size and span still have to meet your local code's span tables (IRC R311.7.5.1 governs stairs off a deck; framing spans are IRC R507.6, adopted in Minnesota with Rule 1309 amendments) or an engineer's stamp. Use this once you already know your framing plan, to count pieces.
For decking: the calculator figures how many rows of boards it takes to cross the deck's width, using your board's actual face width plus the gap you leave between boards (3/16" is typical for wood; composite manufacturers often spec something different — check yours). Each row runs the length of the deck, so total linear footage is rows times length, converted into whole boards of whatever stock length you buy, with a waste percentage added for cuts and mistakes.
For joists: the count comes from the deck's length divided by your joist spacing (12", 16", or 24" on-center), plus one to close out the run. Each joist is sized up to the nearest common stock length that covers the deck's width. Fastener count is a rough estimate — two fasteners (hidden clips or face screws) at every point a board crosses a joist.
Composite decking often needs tighter joist spacing than wood — check your product's installation guide before finalizing a framing plan; some composites require 12" on-center at angles or stair treads even when 16" is fine in the field.
Frequently asked
Does this size my joists for structural span?
No. It counts pieces once you've already chosen a joist size and spacing that meets your local code's span tables. It doesn't check whether that spacing is adequate for your joist size and species.
Hidden clips or face screws — does it matter for the math?
Not for the board or joist count, just for which hardware you're counting at each crossing. Hidden clips generally cost more per board but leave no visible fastener heads.
Questions about a project? Contact us.