Deck Materials Example: Boards, Joists, and Posts for a 12 x 16 Deck
October 21, 2026
For a 12 × 16 ft deck with boards running along the 16-foot length, each board is 16 feet long and you need enough rows to cover the 12-foot width. With nominal 6-inch decking (5.5 inches actual) and a 1/8 inch gap, each row takes 5.625 inches, so you need 144 ÷ 5.625 ≈ 25.6, which rounds up to 26 boards. Joists running the 12-foot dimension at 16 inches on center need 192 ÷ 16 + 1 = 13 joists.
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Divide the width of the deck in inches by the board width plus gap. 144 in ÷ 5.625 in = 25.6, so buy 26 boards, then add 5% to 10% for waste, culls, and cuts: about 28 boards. If the boards must be spliced because they are shorter than the deck, plan for breaks to land on joists and stagger them.
Square footage is 192, and one 16-foot board covers 16 × 5.5 ÷ 12 = 7.33 square feet, so 26 boards cover about 191 square feet, matching the area.
Joists and Spacing
Joists support the deck boards and are typically spaced at 16 inches on center for standard wood decking, or 12 inches for diagonal board patterns and some composite products. Wider spacing, such as 24 inches, depends on the decking product's rating.
Count joists by dividing the length in inches by the spacing and adding one for the end: 192 ÷ 16 = 12, plus 1 equals 13. Add rim or band joists around the outside, and double the joists where required by local code. Joist size depends on span: check your span tables or building department.
| Joist spacing | Joists for 16 ft length | Typical use |
|---|---|---|
| 12 in on center | 17 | Diagonal boards, some composites |
| 16 in on center | 13 | Standard decking |
| 24 in on center | 9 | Only where decking is rated for it |
Posts, Footings, and Fasteners
Post count depends on beam span and joist size. A 12 × 16 deck with a beam on the outer edge often uses 3 to 4 posts along the beam, each on a concrete footing below the frost line. Footing depth varies by region, from 12 inches in warm climates to 48 inches or more in cold ones.
For fasteners, estimate about 2 screws per board per joist. With 26 boards crossing 13 joists, that is 26 × 13 × 2 = 676 screws, so buy roughly 750 for waste. Deck codes, permits, and railings vary by location, so confirm requirements before building.
Frequently Asked Questions
How many deck boards do I need for a 12x16 deck?
About 26 boards of 16 ft with 5.5-inch boards and 1/8 inch gaps, plus 5% to 10% for waste.
How far apart should deck joists be?
Typically 16 inches on center for standard decking, and 12 inches for diagonal layouts, unless the decking product allows more.
How many screws per square foot of decking?
Roughly 3.5 screws per square foot for 5.5-inch boards on 16-inch joist spacing.
Do I need a permit?
Often yes, particularly for attached or elevated decks. Check with your local building department.