How Many Boards for a 12x12 Deck?
Deck boards to buy
20 16 ft boards
144 square feet, 5/4 by 6 decking at a quarter inch gap, 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 length12 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 buy20 16 ft boards
| Deck area | 144 sq ft |
|---|---|
| Board rows across the width | 26 |
| Linear feet of decking | 312 lf |
| Boards at 16 ft | 20 |
| Joists at 16 in on center | 10 |
The material list this produces
| Deck boards, 16 ft | 20 |
|---|---|
| Joists, 12 ft | 10 |
| Joist hangers, each | 20 |
| Deck screws, lb | 5 |
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 | 39 8 ft boards |
| 12 ft boards | 26 12 ft boards |
| 16 ft boards | 20 16 ft boards |
| 20 ft boards | 16 20 ft boards |
What else matters here
The board count comes from linear feet, not from area. Twelve feet across at five and a half inches plus a quarter inch gap is 26 rows, each 12 feet long, which is 312 linear feet of decking. Cut from 16 foot stock that is 20 boards with usable offcuts.
Buying 12 foot boards instead would mean 26 boards with no offcut at all, which sounds tidier and usually is not. Decking is sold with a length tolerance and a crown, and a board that arrives an inch short of 12 feet is scrap rather than a board you trim.
Ten joists at 16 inches on center carries a standard residential deck at this span. Going to 12 inch centers is what you do for diagonal decking or for composite boards, most of which are rated for 16 inch spans straight and 12 inch on a diagonal.
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 12x12 deck?
About 20 boards of 5/4 by 6 at 16 feet, which is 312 linear feet of decking across 26 rows.
How many joists for a 12x12 deck?
Ten joists at 16 inches on center, plus the rim joists. Composite decking on a diagonal usually needs 12 inch centers instead.
How much does a 12x12 deck cost?
Material is the part this calculator settles. Labor, footings, railing and permits sit on top of it and vary far more by location than the lumber does.
The deck calculator takes any dimensions you like and hands back the same list.