How Many Boards for a 12x20 Deck?
Deck boards to buy
33 16 ft boards
240 square feet, 520 linear feet of decking, joists 16 inches on center.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Deck length20 ft
- Deck width12 ft
- Board face width5.5 in
- Gap between boards0.25 in
- Board length you buy16 ft
- Joist spacing on center16 in
Deck boards to buy33 16 ft boards
| Deck area | 240 sq ft |
|---|---|
| Board rows across the width | 26 |
| Linear feet of decking | 520 lf |
| Boards at 16 ft | 33 |
| Joists at 16 in on center | 16 |
The material list this produces
| Deck boards, 16 ft | 33 |
|---|---|
| Joists, 12 ft | 16 |
| Joist hangers, each | 32 |
| Deck screws, lb | 8 |
Board length compared
Same deck, four board lengths.
| Board length | Deck boards to buy |
|---|---|
| 8 ft boards | 65 8 ft boards |
| 12 ft boards | 44 12 ft boards |
| 16 ft boards | 33 16 ft boards |
| 20 ft boards | 26 20 ft boards |
What else matters here
Twenty foot rows cut from 16 foot stock have butt joints.
Sixteen joists at 16 inch centers, cut to 12 feet.
What this calculator assumes
- A nominal 2x6 board is 5.5 inches of actual face. Nominal sizes are not real sizes, which is where most deck orders go wrong.
- Joist count is the span across the deck width at the spacing given, plus one for the last joist.
- Waste is not added. Add 5 to 10 percent if the deck is not a plain rectangle.
Questions people ask
How many deck boards for a 12x20 deck?
About 33 boards of 5/4 by 6 at 16 feet, covering 520 linear feet across 26 rows.
The deck calculator takes any dimensions you like and hands back the same list.