Materials for a 12×20 deck
29 deck boards (20 ft)
for 240 sq ft: 26 rows of 5½ in boards with a ⅛ in gap, on 16 joists, with 10% extra.
For a 12×20 foot deck, the boards run along the 20 ft side and the joists span the 12 ft side.
Materials for a 12×20 deck
| Deck area | 240 sq ft |
|---|---|
| Deck boards (5½ in × 20 ft) | 29 |
| Linear feet of decking | 520 ft (+10% = 572 ft) |
| Joists at 16 in on center | 16 × 12 ft |
| Joists at 12 in on center | 21 × 12 ft |
| Rim joists | 2 × 20 ft |
| Deck screws | about 832 |
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
- 12×18 deck
- 10×20 deck
- 14×20 deck
- 12×16 deck
- 12×24 deck
- 12×14 deck
- 8×20 deck
- 16×20 deck
- 12×12 deck
- 10×12 deck
- 18×20 deck
- 8×12 deck
Questions
- How many deck boards do I need for a 12×20 deck?
- 29 boards 20 ft long (5½ in wide), laid in 26 rows, including 10% extra.
- How many joists for a 12×20 deck?
- 16 joists 12 ft long at 16 in on center, or 21 at 12 in on center.
- How many screws for a 12×20 deck?
- About 832 deck screws: two per board at each joist. A 5 lb box holds roughly 350 to 450 screws.
- How much does a 12×20 deck cost?
- Decking boards alone run about $915 in pressure-treated pine or $2,288 in composite. A finished 240 sq ft deck built by a contractor typically costs $7,200 to $14,400.