Deck board calculator: how many deck boards do I need?
35 deck boards
192 square feet of surface · for 12 × 16 ft
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
35 deck boards
192 square feet of surface
A 12 by 16 ft deck takes 35 boards of 5.5 inches by 12 feet with a 1/8 inch gap between them. Change the board size and the gap to the ones you are buying.
A worked example
A 10 by 20 ft deck in 5.5 in by 16 ft boards, a 3/16 in gap and a 5% waste allowance needs 28 boards. 200 square feet, and a 5.5 in by 16 ft board with a 3/16 in gap covers about 7.6 square feet, so 27 boards plus the 5% allowance is 28.
What else it is called
Deck boards are sold as 5/4 by 6 and 2 by 6 in wood, and composite and PVC boards in the same 5.5 inch actual width. The count depends on the width and length you pick, not the material. Boards come in set lengths, so pick the one that spans your joists with the least waste.
Common sizes
| Area | 5.5 in × 8 ft | 5.5 in × 12 ft | 5.5 in × 16 ft | 5.5 in × 20 ft | 3.5 in × 12 ft |
|---|---|---|---|---|---|
| 8 × 8 ft — 64 sq ft | 18 | 12 | 9 | 7 | 18 |
| 10 × 10 ft — 100 sq ft | 27 | 18 | 14 | 11 | 28 |
| 10 × 12 ft — 120 sq ft | 32 | 22 | 16 | 13 | 34 |
| 12 × 12 ft — 144 sq ft | 39 | 26 | 20 | 16 | 40 |
| 12 × 16 ft — 192 sq ft | 52 | 35 | 26 | 21 | 53 |
| 16 × 20 ft — 320 sq ft | 86 | 57 | 43 | 35 | 89 |
| 20 × 20 ft — 400 sq ft | 107 | 72 | 54 | 43 | 111 |
Pieces, rounded up, with a 0.125 in joint and no waste allowance added.
Where the numbers come from
- A board covers its width plus the gap, times its length: a 5.5 inch board with a 1/8 inch gap is 5.625 inches wide, times 12 feet. The count is the deck area divided by that coverage, rounded up, so no figure here is ours to source — you tell the page the board and the gap.
This counts the deck surface you type in. It does not count the joists, the rim, the fascia or the stairs, and it does not add boards for a picture-frame border or a diagonal layout — those cut more pieces, so raise the waste allowance. Decking is sold by the board, so this is the count to buy.
By Javier Miralles · Last updated . How this site is made.
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