How Many Boards for a 4x8 Deck?
Deck boards to buy
9 8 ft boards
32 square feet, boards running the 8 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 length8 ft
- Deck width4 ft
- Board face width5.5 in
- Gap between boards0.25 in
- Board length you buy8 ft
- Joist spacing on center16 in
Deck boards to buy9 8 ft boards
| Deck area | 32 sq ft |
|---|---|
| Board rows across the width | 9 |
| Linear feet of decking | 72 lf |
| Boards at 8 ft | 9 |
| Joists at 16 in on center | 7 |
The material list this produces
| Deck boards, 8 ft | 9 |
|---|---|
| Joists, 4 ft | 7 |
| Joist hangers, each | 14 |
| 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 | 9 8 ft boards |
| 12 ft boards | 6 12 ft boards |
| 16 ft boards | 5 16 ft boards |
| 20 ft boards | 4 20 ft boards |
What else matters here
Nine rows, each one a single 8 foot board, no cuts and no joints. That is the cleanest a deck order ever gets, and it happens because the run matches a stocked board length exactly.
Running the boards the other way would mean 17 rows of 4 feet, which is 68 linear feet instead of 72 and looks cheaper on paper. It is not, because 17 rows means 17 board ends to fasten and a lot more cutting, and because the joists would then run the long way and need a beam under them at mid span.
The direction the decking runs decides the direction the joists run, and joists want to be short. Boards across the narrow way with joists spanning the long way is how a 4 by 8 turns into a bouncy deck that needed a beam nobody put in.
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 4x8 deck?
Nine boards of 5/4 by 6 at 8 feet, one per row, with no cutting.
Which way should deck boards run?
Across the joists, which means the joists should be the short span. On a 4 by 8 that is boards running the 8 foot way over 4 foot joists.
How many joists for a 4x8 deck?
Seven at 16 inches on center along the 8 foot run, each one 4 feet long.
The deck calculator takes any dimensions you like and hands back the same list.