Why this list goes past deck boards
Surface-board calculators answer the easiest question and leave the expensive structure behind. This takeoff starts with the same dimensions, then follows the load path: decking to joists, joists to beams, beams to posts, and posts to footing pads. Hardware and waterproofing sit beside the member they protect.
Spacing is a product rule and a span rule
Composite boards installed straight can sit on joists at 16 in o.c.; diagonal layouts tighten that to 12 in o.c.. That spacing determines the number of joists. Joist depth is a separate lookup against the verified IRC span table—so a 12 ft span does not get rounded down to a convenient 2×8.
Why footing depth stays open
The deck dimensions determine tributary area and a prescriptive bearing-pad size. They do not reveal the local frost line. Until that local value is entered, concrete and tube quantities remain marked “confirm” instead of becoming a confident-looking guess.
Questions before the lumber run
What does this deck material calculator include?
It calculates the surface boards and the framing and site materials people commonly miss: joists, rim boards, beams, posts, footing pads, form tubes, concrete, connectors, flashing, fasteners, waterproofing tape and fascia.
How far apart should deck joists be?
For the composite system used here, straight boards are limited to 16 inches on center and diagonal boards to 12 inches on center. The joist size is then selected from the 2021 IRC Southern Pine span table.
How deep should deck footings be?
The correct depth depends on the local frost line and code amendments. This calculator does not guess it. Enter the locally required depth to unlock the concrete and form-tube quantities.
Can I use the list without creating an account?
Yes. The complete result is visible, printable and checkable without signup, an email gate, a paywall or a watermark.