How Many Boards for a 16x20 Deck?
Deck boards to buy
43 16 ft boards
320 square feet, 680 linear feet of decking, joists 16 inches on center.
When the figures look right, the deck material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
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 width16 ft
- Board face width5.5 in
- Gap between boards0.25 in
- Board length you buy16 ft
- Joist spacing on center16 in
Deck boards to buy43 16 ft boards
| Deck area | 320 sq ft |
|---|---|
| Board rows across the width | 34 |
| Linear feet of decking | 680 lf |
| Boards at 16 ft | 43 |
| Joists at 16 in on center | 16 |
The material list this produces
| Deck boards, 16 ft | 43 |
|---|---|
| Joists, 16 ft | 16 |
| Joist hangers, each | 32 |
| Deck screws, lb | 10 |
Board length compared
Same deck, four board lengths. Longer boards mean fewer end joints and more offcut risk.
| Board length | Deck boards to buy |
|---|---|
| 8 ft boards | 85 8 ft boards |
| 12 ft boards | 57 12 ft boards |
| 16 ft boards | 43 16 ft boards |
| 20 ft boards | 34 20 ft boards |
What else matters here
Three hundred and twenty square feet is a large residential deck, and at this size the framing plan matters more than the board count. Sixteen joists at 16 inch centers span the 16 foot direction, and the 20 foot run needs at least one intermediate beam line unless the joists run the other way.
Decide the board direction before ordering. Boards running the 20 foot way need joints; boards running the 16 foot way do not, but then the joists run the 20 foot direction and the framing gets heavier. On most decks this size, boards run the 16 foot way parallel to the house.
Ten pounds of screws is around 1,400 fasteners at two per joist crossing. That is a day with an impact driver, and it is exactly the size of job where hidden fastener clips start to look worth their price.
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 16x20 deck?
About 43 boards of 5/4 by 6 at 16 feet, covering 680 linear feet across 34 rows.
Do I need a beam in the middle of a 16x20 deck?
Almost always. Either the joists are short and there is an intermediate beam, or the joists span the full distance and are sized up accordingly. The span table decides which.
How long does it take to build a 16x20 deck?
For a two person crew, roughly a week for framing and decking with footings already cured, plus railing and stairs. Weather and inspection scheduling usually add more than the work does.
The deck calculator takes any dimensions you like and hands back the same list.