How Many Boards for a 10x12 Deck?
Deck boards to buy
21 12 ft boards
120 square feet, 21 rows running the 12 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 length12 ft
- Deck width10 ft
- Board face width5.5 in
- Gap between boards0.25 in
- Board length you buy12 ft
- Joist spacing on center16 in
Deck boards to buy21 12 ft boards
| Deck area | 120 sq ft |
|---|---|
| Board rows across the width | 21 |
| Linear feet of decking | 252 lf |
| Boards at 12 ft | 21 |
| Joists at 16 in on center | 10 |
The material list this produces
| Deck boards, 12 ft | 21 |
|---|---|
| Joists, 10 ft | 10 |
| Joist hangers, each | 20 |
| Deck screws, lb | 4 |
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 | 32 8 ft boards |
| 12 ft boards | 21 12 ft boards |
| 16 ft boards | 16 16 ft boards |
| 20 ft boards | 13 20 ft boards |
What else matters here
Twenty one rows at 12 feet, 252 linear feet, twenty one boards with nothing to cut. The framing is where the thinking goes on this one.
A 10 by 12 attached to the house needs a beam and posts at the outer edge, and the number of footings comes from the beam span rather than from the deck size. A doubled 2x10 beam carries roughly 8 to 9 feet between posts in common species, so a 12 foot outside edge is two posts at the ends and often a third in the middle.
Each of those posts sits on a footing that has to reach below the frost line, which is a local number: about 12 inches in the south, 42 to 48 in the upper midwest and parts of New England, and deeper in a few places. A footing that stops short of it heaves in winter and takes the deck with it, and this is the item most often shortened when the digging gets hard.
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 10x12 deck?
Twenty one boards of 5/4 by 6 at 12 feet, one per row, with no cutting.
How many footings does a 10x12 deck need?
It comes from the beam span, not the deck area. A doubled 2x10 beam spans roughly 8 to 9 feet, so a 12 foot edge usually takes three posts and three footings.
How deep do deck footings need to be?
Below the local frost line, which ranges from about a foot in the south to four feet or more in the north. The building department has the number for your area.
The deck calculator takes any dimensions you like and hands back the same list.