Materials for a 20×20 deck
48 deck boards (20 ft)
for 400 sq ft: 43 rows of 5½ in boards with a ⅛ in gap, on 16 joists, with 10% extra.
For a 20×20 foot deck, the boards run along the 20 ft side and the joists span the 20 ft side.
Materials for a 20×20 deck
| Deck area | 400 sq ft |
|---|---|
| Deck boards (5½ in × 20 ft) | 48 |
| Linear feet of decking | 860 ft (+10% = 946 ft) |
| Joists at 16 in on center | 16 × 20 ft |
| Joists at 12 in on center | 21 × 20 ft |
| Rim joists | 2 × 20 ft |
| Deck screws | about 1,376 |
Framing sizes (joist depth, beams, posts and footings) depend on spans and local code; check your building department’s deck guide before you build.
Change the numbers
Other deck sizes
- 18×20 deck
- 16×20 deck
- 20×24 deck
- 14×20 deck
- 12×20 deck
- 10×20 deck
- 8×20 deck
- 16×24 deck
- 18×24 deck
- 14×24 deck
- 18×18 deck
- 12×24 deck
Questions
- How many deck boards do I need for a 20×20 deck?
- 48 boards 20 ft long (5½ in wide), laid in 43 rows, including 10% extra.
- How many joists for a 20×20 deck?
- 16 joists 20 ft long at 16 in on center, or 21 at 12 in on center.
- How many screws for a 20×20 deck?
- About 1,376 deck screws: two per board at each joist. A 5 lb box holds roughly 350 to 450 screws.
- How much does a 20×20 deck cost?
- Decking boards alone run about $1,514 in pressure-treated pine or $3,784 in composite. A finished 400 sq ft deck built by a contractor typically costs $12,000 to $24,000.