BuildCalc Guides · Decking
How Many Deck Screws Per Board?
Build a deck and you will buy more screws than you think. Here is the per-board count, screw lengths and what an average deck needs.
The math
Two factors decide the count: how many joists the board crosses, and how many screws per joist.
- Joist count = board length ÷ joist spacing + 1. A 12-ft board on 16-inch OC: 144 ÷ 16 + 1 = 9 joists.
- Screws per joist: 2. One screw on each side of the board, into the same joist.
- Total per board = 9 × 2 = 18 screws per 12-ft board.
- Whole deck: count boards, multiply by screws per board, add 10 percent for dropped/stripped screws.
By board length and joist spacing
16-inch OC is the standard for most decks. 12-inch OC is used for diagonal patterns, picture-frame borders, or composite decking that requires it.
| Board | Joists (16 OC) | Screws (16 OC) | Joists (12 OC) | Screws (12 OC) |
|---|---|---|---|---|
| 8 ft | 7 | 14 | 9 | 18 |
| 10 ft | 8 | 16 | 11 | 22 |
| 12 ft | 9 | 18 | 13 | 26 |
| 14 ft | 11 | 22 | 15 | 30 |
| 16 ft | 12 | 24 | 17 | 34 |
| 20 ft | 15 | 30 | 21 | 42 |
Screw sizes for decking
- 2-1/2 inch — the workhorse. Use for 5/4 (about 1 inch actual) composite or wood decking. Penetrates 1-1/2 inches into the joist below.
- 3 inch — for thicker 2× lumber decking (uncommon residentially, but used for docks/heavy use).
- 1-5/8 inch — fascia, rail trim, stair risers. Anywhere you are screwing a thin board into a 1× backing.
- Star drive (T20 or T25) over Phillips — way fewer cam-outs. Worth the small upcharge, especially with a battery driver.
How much to buy
By deck size, with 10 percent waste for stripped/dropped screws:
- 100 sq ft (10 × 10): ~550 screws → 1 box of 5 lb (~750 count).
- 200 sq ft (10 × 20): ~1,100 screws → 1 box of 5 lb plus a spare 1 lb box.
- 400 sq ft (20 × 20): ~2,200 screws → 3 boxes of 5 lb.
- Hidden fasteners: clip systems use 2 clips per joist crossing instead of 2 screws, same overall count but no visible screw heads on the deck face.
Calculate for your own deck
Punch in deck dimensions, joist spacing, board length and orientation — BuildCalc returns boards, screws, and joists for the whole frame.
Open the decking calculator →FAQ
How many deck screws do I need per board?+
Two screws per joist crossing. On a standard 16-inch on-center joist layout, a 12-foot board crosses 9 joists = 18 screws per board. A 16-foot board crosses 12 joists = 24 screws.
How many deck screws per square foot?+
On 16-inch on-center joists with 5-1/2 inch wide boards, plan for about 5 screws per square foot of deck. A 200 sq ft deck takes about 1,000 screws — call it a 5 lb box.
What length deck screws should I use?+
2-1/2 inch for 5/4 (~1 inch actual) composite or wood decking on 2× joists — penetrates the joist about 1-1/2 inches. 3 inch for 2× decking. 1-5/8 inch for thinner under-rail trim or fascia. Match the head type to your decking — most composites need hidden fasteners or color-matched screws.
Should I use stainless or coated deck screws?+
For pressure-treated lumber, use either stainless or screws specifically rated for ACQ-treated wood (T-50 hot-dip or ceramic coating). Standard zinc-plated screws corrode in 1 to 2 years in PT lumber because of the copper-based treatment. Stainless costs 3× more but lasts 30+ years.
Are deck screws better than nails?+
For deck boards: yes. Screws hold under thermal expansion/contraction cycles and don't pop out like ring-shank nails will after a few winters. For framing (joists to ledger, hangers): structural screws or proper joist-hanger nails — never deck screws, which lack the shear strength.
Can I use hidden fasteners instead of face-screwing?+
Yes — most composite manufacturers (Trex, TimberTech, Fiberon) sell board-edge clip systems that hide every fastener. Costs more per square foot than face-screwing but the finished look is clean. Hidden systems generally use 2 clips per joist on the board edge, same count as 2 screws.
Related guides
- How many stair stringers do I need? — for the steps off the deck.
- How many bags of concrete for a sonotube? — for the deck footings underneath.