How Many Deck Screws Do I Need? Chart by Deck Size

Use two screws wherever a deck board crosses a joist. With standard 5.5 in boards on joists 16 in apart, that's about 3.5 to 4 screws per square foot: a 12 × 12 ft deck takes 520 screws, and a 10 × 10 ft deck 396. Joists 12 in apart need about a third more.

Rows = width ÷ (board width + gap). Screws = rows × joists × 2. Dashed lines are joists.

Deck screws by deck size

Counts are for 5.5 in boards with 3/16 in gaps, two screws per board at every joist, and boards as long as the deck (no joins). The last column adds 5% for dropped and stripped screws and rounds up to packs of 350.

Deck screws for common deck sizes
Deck (length × width)	Joists at 16 in	Joists at 12 in	Packs of 350 (16 in, +5%)
8 × 8 ft	238	306	1
10 × 10 ft	396	484	2
12 × 12 ft	520	676	2
16 × 12 ft	676	884	3
20 × 12 ft	832	1,092	3
20 × 16 ft	1,088	1,428	4

Metric: 140 mm boards with 5 mm gaps
Deck (length × width)	Joists at 450 mm	Joists at 400 mm
3 × 3 m	336	378
3.6 × 3.6 m	450	500
4.8 × 3.6 m	600	650
6 × 4 m	840	896

How to work it out

Rows of boards: the deck's width ÷ (board width + gap), rounded up. A 12 ft (144 in) deck: 144 ÷ 5.6875 = 25.3, so 26 rows.
Joists: the deck's length ÷ joist spacing, plus one. 144 ÷ 16 = 9, so 10 joists.
Crossings: rows × joists = 26 × 10 = 260.
Screws: two per crossing = 520. Add about 5% spare: 546.

The deck board calculator does this for any size, board width and joist spacing, and adds the screws to your shopping list.

Screws per square foot

As a rule of thumb, allow about 3.5 to 4 screws per square foot on joists 16 in apart and 4.5 to 5 on joists 12 in apart, with 5.5 in boards. Narrower boards mean more rows and more screws. One fastener supplier puts a 10 × 10 ft deck at 350 to 500 screws, which matches these counts.

What the count leaves out

Butt joints. Where two boards meet over a joist, each board end gets its own two screws: add 2 per join.
Picture-frame borders and stairs. Count these separately: each tread crosses every stringer.
Hidden clips. Clip systems are counted per clip, not per screw. Use the coverage printed on the box instead.
Framing. Joist hangers and ledger fixings use their own connectors and structural screws, not deck screws.

Which length?

Deck screws between 2½ and 3 in long suit most decks. A screw needs to go through the board and well into the joist, so thicker boards take longer screws. Use screws rated for outdoor use and for your board: composite boards and treated wood often need their own type, and many board makers specify one.

Common mistakes

Counting per board, not per crossing. A board 12 ft long on joists 16 in apart crosses 10 joists, so it takes 20 screws, not 4.
Using the nominal board width. A "6 inch" board is about 5.5 in wide, so using 6 in undercounts the rows and the screws.
Forgetting the joist at each end. Joists are spaces plus one.