Question 1

How do I calculate how many deck boards I need?

Accepted Answer

Start by calculating the deck area (length x width). Divide the deck width by the effective board width (board width + gap) to get the number of rows. Divide the deck length by the board length to get boards per row. Multiply rows by boards per row. For example, a 12x16 ft deck with 5.5 inch boards (including 1/8 inch gap) needs 27 rows of 16 ft boards, totaling 27 boards plus about 10 percent waste = 30 boards.

Question 2

What gap should I leave between deck boards?

Accepted Answer

Standard gap between pressure-treated deck boards is 1/8 inch (3 mm) for wet boards (they will shrink) or 1/4 inch (6 mm) for kiln-dried or composite boards (they will not shrink). Wet PT lumber shrinks about 1/8 inch when fully dry, so starting at 1/8 inch gives a final 1/4 inch gap. Composite decking needs consistent gaps as specified by the manufacturer - typically 3/16 to 1/4 inch.

Question 3

What size deck boards should I buy?

Accepted Answer

The most common deck board is 5/4x6 (actually 1 inch x 5.5 inches) pressure-treated or composite, which provides a good balance of width, weight, and cost. Standard 2x6 works for longer spans but is heavier and more expensive. For hot tubs, heavy loads, or 2-foot joist spacing, use 2x6 instead of 5/4. 2x4 boards are used for narrow ladder-style decks and some tropical hardwood installations.

Question 4

How many screws do I need per deck board?

Accepted Answer

For face-screwed decking, use 2 screws per board at each joist crossing. A typical 16-foot board spans 10 or 11 joists (at 16 inch on-center), so you need 20 to 22 screws per board. For a 12x16 deck with 30 boards, plan on about 650 screws (use 3 inch deck screws). With hidden fastener clips, screws go into the board edges, and you need 1 clip per joist per board.

Question 5

Should I use hidden fasteners or screws on my deck?

Accepted Answer

Hidden fasteners give a cleaner look without visible screw heads, but cost 2 to 3 times more and take longer to install. They work best with grooved-edge composite decking. Face-screwing with quality stainless steel or coated deck screws is cheaper, faster, and holds boards more securely against cupping. For visible, premium decks, hidden fasteners are worth the extra cost; for utility decks, standard screws work fine.

Question 6

How much extra deck board should I buy for waste?

Accepted Answer

For a straight board pattern with square deck edges, buy 10 percent extra. For diagonal or angled decks (45 degree boards), buy 15 to 20 percent extra because each cut creates waste. Herringbone patterns need 20 to 25 percent extra. Picture frame borders add another 5 percent. Pros recommend ordering 10 percent over the calculated minimum even for the simplest deck, to account for defects and future repairs.

Question 7

What is the difference between 5/4 and 2x decking?

Accepted Answer

5/4 decking (pronounced five-quarter) is 1 inch thick x 5.5 inches wide (nominally 5 quarters of an inch thick, actual 1 inch). It is lighter, cheaper, and easier to install than 2x6 decking (1.5 x 5.5 inches actual). 2x decking is stronger and spans further between joists. Use 5/4 over joists spaced 16 inches on-center or less; use 2x6 for 24 inch joist spacing or where extra strength is needed.

Material	Gap	Reason
Pressure-treated (wet)	1/8 in (3 mm)	Will shrink when dry
PT kiln-dried / hardwood	1/4 in (6 mm)	Minimal shrinkage
Composite / PVC	3/16 in (5 mm)	Per manufacturer spec

Deck Board Calculator

Deck Dimensions

Board Specs

Pattern

Fasteners

Fasteners

Decking Cost

Shopping List

How to Calculate Deck Boards

Rows and Boards Formula

Board Gap Sizes

Fastener Options

Frequently Asked Questions

Deck Dimensions

Board Specs

Pattern

Fasteners

Fasteners

Decking Cost

Shopping List