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How many deck boards do I need? (12×16 example)

Short answer: Rows of decking = deck width in inches ÷ (board width + gap). A 12×16 deck with 5.5-inch boards and 1/8-inch gaps needs 26 rows. With 16-ft boards and 10% waste, buy 29 boards. Joists at 16 inches on center along the 16-ft side take 13 joists, and plan about 680 deck screws.

The formula

Rows = deck width (in) ÷ (board width + gap), rounded up
Boards per row = deck length ÷ board length, rounded up
Boards to buy = rows × boards per row × (1 + waste)
Joists = (deck length in inches ÷ joist spacing) + 1
Screws = rows × joists × 2

A "5/4×6" or "2×6" deck board is 5.5 in wide. Use 10% waste for straight decking, and 15% or more for diagonal or picture-frame patterns.

Worked example

12 × 16 deck, boards running the 16-ft way, 5.5-in boards, 1/8-in gaps, 16-ft boards, joists 16 in on center, 10% waste:

• Rows: 144 ÷ 5.625 = 25.6 → 26
• Boards: 26 × 1 × 1.10 = 28.6 → 29 boards (16 ft)
• Joists: 192 ÷ 16 + 1 = 13
• Screws: 26 × 13 × 2 = 676

FAQ

How much gap between deck boards?

About 1/8 inch (a 16d nail) for dry wood and composite, unless the maker says otherwise. Pressure-treated boards installed wet are often butted tight because they shrink as they dry.

What joist spacing do I need?

16 inches on center is standard for most wood and composite decking. Many composites require 12 inches on center for diagonal installs. Check the decking manufacturer.

How many screws per square foot?

Roughly 320–350 screws per 100 sq ft with 5.5-inch boards at 16-inch joist spacing, which is 2 screws at every joist crossing.