How this calculator works
This runs our deck board, deck stain and footing calculators on one set of measurements. The number of rows is the deck width divided by a board plus its gap, the boards are the rows times the length with waste divided by the board length, and the joists are spaced along the length plus one. Each board is screwed at every joist it crosses.
Worked example: a 16 × 12 ft deck in 5½ inch boards with 1/8 inch gaps and 16 ft boards: 26 rows, so 29 boards of 16 ft with 10% waste; 13 joists of 12 ft at 16 inch centers; about 676 screws; 6 footings of 12 inches by 3 ft take 26 bags of 80 lb concrete; and 1 gallon of stain covers it once.
Deck boards and joists by size (16 ft boards, 16 in joists, 10% waste)
5½ in boards with 1/8 in gaps.
| Deck | Rows | Boards of 16 ft | Joists | Screws |
|---|---|---|---|---|
| 10 × 10 ft | 22 | 16 | 9 | 396 |
| 12 × 12 ft | 26 | 22 | 10 | 520 |
| 16 × 12 ft | 26 | 29 | 13 | 676 |
| 16 × 16 ft | 35 | 39 | 13 | 910 |
| 20 × 16 ft | 35 | 49 | 16 | 1,120 |
Tips before you buy
- Buy boards as long as the deck if you can. Butt joints are weak points and must land on a joist.
- Pressure-treated boards shrink as they dry: lay them close to flush. Composite boards need the gap the maker specifies.
- Joist size is set by the span, the wood and your building code, not by this calculator. Check a span table or ask your building department.
- A diagonal pattern or a picture-frame border adds cuts. Allow 15% waste and use joists at 12 inches.
- Put flashing tape on top of the joists so that water between the boards does not rot the framing.
Tools & materials for this project
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Frequently asked questions
How many deck boards for a 12x16 deck?
29 boards of 16 ft, or 39 boards of 12 ft, using 5½ inch boards with 1/8 inch gaps and 10% waste. That is 26 rows across the 12 ft width.
How many joists for a 12x16 deck?
13 joists at 16 inches on center, each 12 ft long. At 12 inch spacing it is 17, and at 24 inches 9. Joist size and span must follow your local code.
How many screws do I need for a deck?
About 676 for a 12 × 16 deck: two for every board at every joist it crosses. Buy extra, since some strip or get dropped.
Does a deck need a building permit?
Usually yes, especially if the deck is attached to a house or stands more than a foot or two above the ground. The permit also brings an inspection of the footings and framing.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.