Deck Material Calculator Guide: Boards, Joists & Fasteners
A complete overview of everything a deck build needs — boards, joists, screws, and footing concrete — and how each is calculated.
A deck isn't a single material order — it's at least four separate quantities that all depend on the same base measurements: deck boards, joists, fasteners, and footing concrete.
The four material categories
- Deck boards: calculated from deck length, width, and the board's actual (not nominal) width, plus a 1/8-inch gap between boards for drainage.
- Joists: spaced at 12, 16, or 24 inches on center depending on your decking product's span rating, running perpendicular to the boards.
- Fasteners: roughly 2 screws per board at every joist crossing, or a per-board clip count for hidden fastener systems.
- Footing concrete: based on post count and footing size — a typical residential footing takes about 2 bags of quick-set concrete.
Why actual board width matters
Lumber is sold under a nominal name (a "1x6") but milled to a smaller actual size (5.5 inches for a 1x6). Using the actual width — not the nominal name — is the single most important input for an accurate board count, since nominal sizing overstates coverage.
Plan before you order
Because these four categories are interdependent (joist spacing affects joist count, which affects screw count), it's worth running the full calculation once with your final dimensions rather than estimating each material separately.
The Deck Material Calculator calculates all four categories together from one set of inputs.