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Deck Material Calculator

Estimate deck boards, joists, screws, railing, and footing concrete for a rectangular residential deck. A permit and structural design are typically required.

Deck
ft
ft
Boards
in
ft
in
%
Framing and support
in
ft

Deck area

192 sq ft

Boards

29

Joists

13

Screws

2.2 lb

Railing

40 ft

Footing concrete

20 bags

Assumptions

  • Rows across the width based on board width plus gap.
  • Boards per row is length divided by board length, rounded up.
  • Deck screws ~350 per pound; ~2 screws per board per joist.
  • Each footing ~1.5 cu ft; ~0.45 cu ft per 60 lb bag of concrete.

Sizing a deck material order

The board count is length across the deck divided by the row width (board width plus gap), times length along the deck divided by the board length you can buy locally. Add a waste percentage for cuts and offcuts. The joist count is a function of length divided by joist spacing plus one. Screws come out to a couple per board per joist crossing, in pounds.

Footings and permits

Footings are the piece most people underestimate. Frost depth, soil bearing, and post loading control size and spacing, and code enforcement takes the deck ledger connection to the house very seriously. Do the sizing math to shop materials, then confirm the structural plan against your local building department before you dig.

Composite versus lumber

Composite boards last longer, require closer joist spacing (often 12 in on center for diagonal or picture-frame patterns), and cost roughly two to three times pressure treated wood on the boards alone. The framing under either material is essentially the same.

Frequently asked questions

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Educational estimates only. Not financial, tax, or legal advice.

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