How Many Deck Boards Do I Need for a 12x16 Deck?
For a 12 × 16 foot deck with boards running the 12-foot direction, divide the 16-foot width by the 5.5-inch board width: 16 ÷ (5.5/12) = 34.9 → 35 boards exact, or 39 with a 10% cutting allowance. The chart below covers other deck widths.
Key Takeaways
- Boards run the 12-ft direction; count spans the 16-ft width.
- A 5.5-inch board covers 5.5/12 = 0.458 ft of width.
- 16 ÷ 0.458 = 34.9 → 35 boards exact.
- Add 10% → order 39 boards.
- Picture-frame borders and stairs need extra boards.
How to Calculate Deck Boards for a 12x16 Deck
Board count comes from the width the boards must span, divided by one board’s width. Gaps between boards are small enough to ignore in the count.
- 1Decide board direction: 12-ft boards run the 12-ft length.
- 2Find the span: 16 ft of width to cover.
- 3Convert board width: 5.5 ÷ 12 = 0.458 ft.
- 4Divide: 16 ÷ 0.458 = 34.9 → 35 boards.
- 5Add 10% waste: 35 × 1.10 = 38.5 → 39 boards.
The Deck Board Formula
The small gaps between boards (about 1/8–1/4 inch) are absorbed by rounding up. For pattern borders, calculate the field and border separately.
Boards = Span (ft) ÷ (Board width in inches ÷ 12)Worked Example: 12 ft × 16 ft Deck
Full math for a 12 × 16 deck with 12-ft boards, plus a chart for other deck widths.
Deck: 12 ft × 16 ft; boards run the 12-ft direction.
Width to span: 16 ft.
Board width: 5.5 ÷ 12 = 0.458 ft.
Exact boards: 16 ÷ 0.458 = 34.9 → 35.
With 10% waste: 35 × 1.10 = 38.5 → 39 boards.
| Deck width spanned | Boards (exact) | With 10% waste |
|---|---|---|
| 12 ft | 27 | 30 |
| 16 ft | 35 | 39 |
| 20 ft | 44 | 49 |
Common Mistakes
- Forgetting stairs, which need their own treads and risers.
- Not accounting for a picture-frame border’s extra boards.
- Butt-joining boards mid-span without planning the stagger.
- Ignoring the ledger and rim joist in the lumber list.
- Ordering exact with no spare for splits and bad grain.
Practical Tips
- Sight down each board and reject badly crowned ones.
- Stagger butt joints over different joists for strength.
- Leave 1/8–1/4 inch gaps for drainage and expansion.
- Pre-drill near board ends to prevent splitting.
- Estimate the full structure with the NOVORY Deck Calculator.
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