How Many Boards for a 4x6 Deck?
Deck boards to buy
5 12 ft boards
24 square feet, boards running the 6 foot way, 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 length6 ft
- Deck width4 ft
- Board face width5.5 in
- Gap between boards0.25 in
- Board length you buy12 ft
- Joist spacing on center16 in
Deck boards to buy5 12 ft boards
| Deck area | 24 sq ft |
|---|---|
| Board rows across the width | 9 |
| Linear feet of decking | 54 lf |
| Boards at 12 ft | 5 |
| Joists at 16 in on center | 6 |
The material list this produces
| Deck boards, 12 ft | 5 |
|---|---|
| Joists, 4 ft | 6 |
| Joist hangers, each | 12 |
| Deck screws, lb | 1 |
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 | 7 8 ft boards |
| 12 ft boards | 5 12 ft boards |
| 16 ft boards | 4 16 ft boards |
| 20 ft boards | 3 20 ft boards |
What else matters here
Nine rows at 6 feet is 54 linear feet, which is five 12 foot boards cut in half with one half left over. Twelve foot stock is the right buy here for the same reason it usually is on small decks: the cut length divides into it exactly.
The decision worth making on a deck this small is whether to hang it off the house at all. A ledger board is the single most common structural failure point on residential decks, and the failure is almost always water rather than fasteners: the flashing was wrong or missing, the sheathing behind it rotted, and the whole thing let go years later.
A 4 by 6 is light enough to stand on its own four posts a few inches clear of the siding, which removes the ledger, the flashing and the lag schedule from the job entirely. It costs two more footings and it takes the house out of the load path.
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 boards for a 4x6 deck?
Five boards of 5/4 by 6 at 12 feet, cut in half, covering 9 rows at 6 feet each.
Should a small deck be attached to the house?
It does not have to be. A freestanding deck on its own posts removes the ledger and its flashing, which is where most deck failures start.
How many joists does a 4x6 deck need?
Six at 16 inches on center across the 6 foot run, including the end joists.
The deck calculator takes any dimensions you like and hands back the same list.