The formula: deck square footage × 2.18 = linear feet of standard 5.5″-wide boards (that factor includes the ⅛–¼″ gap between boards). Divide by your board length, add 10% waste (15% for diagonal decking), and that’s your order.
Worked example: 12×16 deck
192 sq ft × 2.18 = 419 linear ft ÷ 16-ft boards = 26.2 → 29 boards with 10% waste. In 2026 prices that’s roughly $700–$900 in pressure-treated, or $1,900–$2,600 in mid-range composite.
Deck board chart (16-ft boards, 10% waste)
| Deck size | Sq ft | Linear ft | 16-ft boards |
|---|---|---|---|
| 10 × 10 | 100 | 218 | 15 |
| 12 × 12 | 144 | 314 | 22 |
| 12 × 16 | 192 | 419 | 29 |
| 14 × 20 | 280 | 610 | 42 |
| 16 × 20 | 320 | 698 | 48 |
Spacing: the detail that ruins decks
Pressure-treated wood installs tight or nearly tight — wet PT boards shrink to create their own gaps. Kiln-dried wood and composite need a deliberate ⅛–¼″ gap for drainage and expansion (composite manufacturers specify exactly; violating it voids warranties). Buy hidden-fastener clips for grooved composite — they set the gap automatically.
Don’t forget the rest of the order
Boards are only the surface. Per 100 sq ft of deck, plan on ~350 screws (or ~90 hidden clips), plus fascia boards for the visible rim, plus stairs (each tread is more board footage people forget). The deck cost calculator prices the whole build — framing, footings, railing, stairs — and the composite vs wood comparison settles the material question with 25-year math before you order anything.
Board length strategy
Match board length to your deck’s dimension when possible — 16-ft boards on a 16-ft deck means zero butt joints, which look better and leak less. When joints are unavoidable, stagger them across joists like brickwork, never in a line.