How this calculator works. Each board-plus-gap covers 5.75" of width (5.5" face + 1/4" gap), so decking needed = area × 12 ÷ 5.75 ≈ 2.09 linear ft per sq ft, plus your waste factor. Boards = linear feet ÷ board length, rounded up. Screws use the standard 2 per board per joist at 16" joist spacing — about 350 per 100 sq ft.
Decking, board by board
The linear-feet number is the honest way to buy decking, because board length is a layout decision: a 16-ft deck surfaced with 16-ft boards has zero butt joints — the seams that collect water, splinter first, and read as amateur from across the yard. Buy the longest boards that span your deck (or stagger 12s and 16s deliberately), and let the waste factor absorb the cut-offs.
Wood versus composite changes budget more than math: composite runs 2–3× the material cost but skips the staining treadmill. If you're pricing both, our stain calculator shows the recurring side of the wood decision.
Fastener choices
| Fastener | Notes |
|---|---|
| Coated deck screws (2.5"–3") | The default; use coated/stainless rated for treated lumber |
| Hidden clip systems | Grooved composite boards; ≈90 clips per 100 sq ft |
| Stainless steel | Mandatory near salt water; cheap screws streak black |
Buying tips
At the lumber yard, sight down every wood board and reject crowns, twists, and wane — culling at the store is free quality control. Install boards bark-side-down where visible rings allow, and pre-drill ends to stop splits. For composite, order all boards in one batch: color runs vary just like tile dye lots.
Common questions
Does this include the joists and framing?
No — this covers the walking surface and its fasteners. Framing (joists, beams, posts, hangers) is structural and sized by span tables and local code; when in doubt, that part deserves a permit and a plan.
What gap for wood vs composite?
Wet pressure-treated lumber: install tight to 1/8" — it shrinks to a 1/4" gap. Kiln-dried wood: 1/4" from day one. Composite: exactly what the manufacturer's chart says for your temperature at install — it expands with heat, not moisture.
How many screws will I actually use?
Two per joist crossing. At 16" joist spacing, a 16-ft board crosses 13 joists — 26 screws per board. It adds up to roughly 350 per 100 sq ft, which is why buying screws by the small box is a mistake.
Diagonal decking — how much extra?
Add 15% instead of 10%: every board meets the rim at an angle, and the triangular offcuts are rarely reusable. Diagonal also requires 12" joist spacing on most spans — check before committing.