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.
Assumptions to Check
Before ordering materials, confirm the dimensions, product coverage, waste factor, and local installation requirements for your project. Manufacturer coverage tables and local code rules can change the final quantity, especially for structural work, exterior projects, and irregular layouts.
Need an exact number for your specific dimensions?
Use the Deck Calculator →