How many deck boards for a 16×20 deck?
Quick Answer
A 16×20 foot deck (320 sq ft) using 5/4×6 boards at 16 feet long needs approximately 44 boards running the 16-foot direction. With 5.625 inches effective width per board: 240 inches ÷ 5.625 = 42.7 boards. Add 5% waste = 45 boards. If running 20-foot boards: 35 boards with butt joints, or 37 with waste.
Quick Reference Table
| Board size / direction | Boards needed (16×20 deck) |
|---|---|
| 5/4×6 × 16 ft (run 16 ft) | 44–46 boards |
| 5/4×6 × 20 ft (run 20 ft) | 35–37 boards |
| 2×6 × 16 ft | 44–46 boards |
| Composite 6" × 16 ft | 44–46 boards |
| Diagonal layout | +15% more boards |
How to Calculate It Yourself
- 1
Choose board direction: typically the longer dimension. For 16×20, run boards the 20-ft direction using 20-ft boards (fewer seams) or the 16-ft direction using 16-ft boards (less expensive).
- 2
Width to span (boards running 16 ft): 20 ft = 240 inches. 240 ÷ 5.625 = 42.7 boards.
- 3
Add 5% waste: 42.7 × 1.05 = 44.8 → buy 45 boards.
- 4
Total screws: 45 boards × ~28 screws each (16 ft board on 16" OC joists) ≈ 1,260 screws. Buy a 5-lb box.
Pro Tip
On a 16×20 deck, consider running 2-piece boards with a butt joint over a doubled joist rather than splicing on a single joist. Doubled joists (3" wide) give you room to land both board ends properly and prevent the raised-board look of poor splices.
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