How many deck boards for a 12×12 deck?
Quick Answer
A 12×12 foot deck using 5/4×6 deck boards (5.5 inch actual width) with 1/8-inch spacing gaps needs approximately 26–28 boards at 12 feet long. The effective coverage per board is 5.625 inches (5.5" + 0.125" gap). 144 inches ÷ 5.625 = 25.6 boards — buy 28 to account for waste and end cuts.
Quick Reference Table
| Board size | Boards needed (12×12 deck) |
|---|---|
| 5/4×6 at 12 ft | 28 boards |
| 2×6 at 12 ft | 28 boards |
| 5/4×4 at 12 ft | 40 boards |
| Composite 6" at 12 ft | 28 boards |
| Diagonal layout | +15% = 32 boards |
How to Calculate It Yourself
- 1
Determine run direction: boards typically run the long direction. For a 12×12, either direction gives 12 ft boards with no waste.
- 2
Calculate board spacing: actual width + gap = 5.5 + 0.125 = 5.625 inches per board.
- 3
Number of boards: 144 inches (12 ft) ÷ 5.625 = 25.6 → round up to 26. Add 2 for waste = 28 boards.
- 4
Add 10% extra if boards need cutting or any are irregular. Buy 30 for a comfortable buffer.
Pro Tip
For a 12×12 deck, 12-foot boards run perfectly with no length waste — a major advantage. Avoid 16-foot boards (you'd cut 4 feet off every board). Check if your lumber yard stocks 12-foot 5/4×6 — some carry only 10 and 16 foot lengths.
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