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Deck Calculator

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Enter your deck's dimensions to find the decking boards, joists, and fasteners you need.

Deck Calculator

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Deck area192 sq ft
Decking boards needed (5.5" wide)27 boards
Joists needed10 joists
Screws (2 per board/joist crossing)540 screws
Covers decking, joists, and fasteners for the deck surface - not footings, beams, or railing, which depend on your specific structural plan.

The formula

Area = Length x Width Total board linear feet = Area / (Board width in feet) Boards needed = Total linear feet / Board length Joists needed = (Width in inches / Joist spacing) + 1
Example

A 16ft x 12ft deck using 16ft boards, 16-inch joist spacing: area = 192 sq ft, boards ≈ 27, joists ≈ 10.

Step-by-step guide

  1. Enter your deck's overall length and width.
  2. Enter the board length you plan to buy and your joist spacing (16 inches is a common standard).
  3. Read the boards, joists, and screws needed.

Why joist spacing affects more than just the joist count

Joist spacing is a structural decision, not just a material-counting one - it determines how much unsupported span each decking board has to bear between support points, which directly affects how much the deck can flex or sag under weight. Standard residential decking typically calls for 16-inch spacing, though thicker or stronger decking materials sometimes allow wider 24-inch spacing. Changing this number to save on joists without confirming it's appropriate for your specific decking material and expected load is a structural decision worth checking against your decking manufacturer's span table, not just a material-cost tradeoff.

Common mistakes

Forgetting waste - cutting boards to fit around posts or edges creates offcuts, so ordering a small buffer (5-10%) above the calculated amount is common practice.
Not accounting for footings and beams - this calculator covers the decking surface, joists, and fasteners only, not the below-deck support structure.

Frequently asked questions

Does this include footings or support posts?

No - this covers the decking surface, joists, and fasteners between them. Footings, posts, and beams depend on your specific structural design and local building code, which vary by project.

What joist spacing should I use?

16 inches on-center is a common standard for typical residential decking - check your specific decking material's manufacturer span table, since composite and different wood species can have different requirements.

Does board width really matter for the calculation?

Yes - this calculator assumes a standard 5.5-inch wide board (common for 5/4x6 decking). Wider or narrower boards would need proportionally fewer or more boards to cover the same area.

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