Count the boards, joists and posts needed to build a deck.
A deck is three counts, each governed by a different dimension. Decking boards run the length, so the number of them spans the width: divide the width in inches by the board width plus a quarter-inch drainage gap, and round up. Joists run the other way, spaced along the length, and the count is one more than the number of spaces because both ends need one — the classic fencepost error that leaves a builder a joist short. Posts sit on a grid under the beams, conventionally no more than eight feet apart, so the count is the product of the spacings in each direction plus one each way. Joist spacing is a structural decision, not a preference: sixteen inches on centre suits most timber decking, while composite boards and diagonal layouts usually demand twelve.
Deck component counts
Boards = ceiling(width in inches / (board width + 0.25)); joists = floor(length in inches / spacing) + 1; posts = (ceiling(length / 8) + 1) x (ceiling(width / 8) + 1)
Material quantities only, not a structural design. Deck framing, footings, ledger attachment and railings are regulated by building codes and often require a permit and inspection — deck collapses are usually attachment failures. Consult a qualified professional before building.
It is the standard for nominal timber decking laid perpendicular to the joists. Composite boards are less stiff and usually specify twelve inches, and any diagonal layout needs twelve because the span between supports is longer along the diagonal.
Yes. It drains water, allows for seasonal movement and stops debris packing the joint. Pressure-treated timber that is still wet will shrink, so some builders lay it tight and let the gap open naturally.
No. Post size, footing depth, beam span and any attachment to the house are governed by building codes and by soil conditions. Use this for material budgeting and have the structure checked.