Exterior

Deck Calculator: Boards, Joists, Screws and Cost

Deck boards, joists, footings and fasteners from your deck dimensions — plus what pressure-treated versus composite really costs.

Your measurements

16 ft deck boards

29boards

449 linear ft across 26 rows, including 8% waste

Deck area
192 sq ft
Board rows5.5 in boards with a 1/8 in gap
26
Joists12 ft each at 16 in on centre
13
Joist lumber
156 linear ft
Beam lumberDoubled beam, rough allowance
32 linear ft
FootingsSpaced at 8 ft or less — confirm against local code
8
Deck screws~676 screws, 2 per joist crossing
2 lb
RailingRequired above 30 in in most of the US
44 linear ft
Material cost$35–$65 per sq ft, materials only
$6,720 – $12,480
Built costMaterials plus contractor labour
$10,560 – $20,160
  • Decks are permit work almost everywhere, and the inspection is about the ledger connection and footings — not the boards. Get the permit; a bad ledger is the single most common cause of deck collapse.
  • Most composite decking requires 16 in on-centre joists at most, and 12 in for a diagonal layout. Check the specific brand — spanning too far voids the warranty and the boards will feel spongy.
  • Footing depth is set by your local frost line, which ranges from nothing in the far south to 48+ in in northern states.

How this is calculated

  • Board rows are the deck width divided by the actual board width plus a 1/8 in gap. Linear feet is rows × deck length, plus 8% for cuts and butt joints.
  • Joists are the deck length divided by the on-centre spacing, plus one, each running the deck width.
  • Footings are spaced at 8 ft maximum in two rows — a starting point, since span tables and local code decide the real number.
  • Cost ranges are typical 2025–2026 US pricing per square foot, materials only and then materials plus contractor labour.

Quantities are rounded up, because materials are sold in whole units and a second trip costs more than a spare box. Cost figures are typical US ranges and are not a quote — always price against your own supplier.

Frequently asked questions

How much does it cost to build a 16x12 deck?

A 192 sq ft deck runs roughly $3,000–$5,800 in pressure-treated materials, or $6,700–$12,500 in composite. Built by a contractor, expect $6,700–$9,600 pressure-treated and $10,500–$20,000 composite depending on height, railing and site access.

How many deck boards do I need?

Divide the deck width by 5.625 in (a 5.5 in board plus a 1/8 in gap) to get the number of rows, multiply by the deck length for linear feet, then add 8% and divide by the board length you are buying.

How far apart should deck joists be?

16 in on centre is standard for pressure-treated decking laid straight. Composite decking often requires 16 in maximum and 12 in for diagonal layouts — check the manufacturer's span table, because exceeding it voids the warranty.

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