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.
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.
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