How Many Boards for an 8x12 Deck?
Deck boards to buy
17 12 ft boards
96 square feet, 17 rows running the 12 foot way, 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 length12 ft
- Deck width8 ft
- Board face width5.5 in
- Gap between boards0.25 in
- Board length you buy12 ft
- Joist spacing on center16 in
Deck boards to buy17 12 ft boards
| Deck area | 96 sq ft |
|---|---|
| Board rows across the width | 17 |
| Linear feet of decking | 204 lf |
| Boards at 12 ft | 17 |
| Joists at 16 in on center | 10 |
The material list this produces
| Deck boards, 12 ft | 17 |
|---|---|
| Joists, 8 ft | 10 |
| Joist hangers, each | 20 |
| Deck screws, lb | 3 |
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 | 26 8 ft boards |
| 12 ft boards | 17 12 ft boards |
| 16 ft boards | 13 16 ft boards |
| 20 ft boards | 11 20 ft boards |
What else matters here
Seventeen rows at 12 feet, 204 linear feet, seventeen 12 foot boards with no cutting at all on the field.
At this size the deck is hung off the house on a ledger, and the ledger is the part of a deck that actually kills people. Collapses are overwhelmingly ledger failures, and ledger failures are overwhelmingly water: the flashing was missing or run the wrong way, the sheathing behind it went soft, and the fasteners pulled through rot rather than breaking.
Three things make it right. Flash it properly, with the membrane lapped over the top of the ledger and under the house wrap so water runs out rather than in. Fasten it with structural screws or through bolts to the rim joist, never to the sheathing and never with lag screws into nothing. And hold it down from the door threshold so the deck surface sits below the sill.
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 an 8x12 deck?
Seventeen boards of 5/4 by 6 at 12 feet, one per row, with no cutting.
How should a deck ledger be attached?
With structural screws or through bolts into the house rim joist, in the pattern the fastener manufacturer specifies. Not into sheathing, and not with lag screws driven blind.
Why do deck ledgers fail?
Water, almost always. Missing or badly lapped flashing rots the sheathing behind the ledger, and the fasteners then pull through soft wood instead of holding.
The deck calculator takes any dimensions you like and hands back the same list.