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.

  • Free — no sign-up, no credits
  • Rounded to what you actually buy
  • Working shown, so you can check it

Your measurements

16 ft deck boards

29boards

449 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 ft
Beam lumberDoubled beam, rough allowance
32 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 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.

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How this is calculated

  1. 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.
  2. Joists are the deck length divided by the on-centre spacing, plus one, each running the deck width.
  3. Footings are spaced at 8 ft maximum in two rows — a starting point, since span tables and local code decide the real number.
  4. 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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