Wood Screw Size, Length and Gauge Reference
Screw length is the number people get wrong. The rule is simple: a screw should penetrate 2 to 3 inches into the solid wood beyond the board being held.
Standard wood screw sizes
| Designation | Diameter | Typical uses |
|---|---|---|
| #6 × 1-1/4" | 0.122" | Light cabinet hinges, thin material |
| #8 × 1-1/2" | 0.136" | Cabinet backs, drawer bottoms, face frames |
| #10 × 2" | 0.159" | General furniture, face frame to cabinet |
| #12 × 2-1/2" | 0.182" | Structural framing to framing |
| 2-1/2" structural | 0.152" | Decking to joists (not a standard wood screw) |
| 3" structural | 0.180" | Decking at thicker joists, ledger to rim |
Choosing length
| Joining | Recommended length |
|---|---|
| 3/4" plywood into 2x4 | 1-1/4" |
| 1/2" plywood into 2x4 | 1-1/2" |
| ¾" plywood into 2x4 | 2" |
| Deck board (1") into 2x6 joist | 2-1/2" structural |
| 2x4 framing into 2x4 plate | 3" |
Gauge and head
- Gauge is the number printed on the head — lower number means thicker. For structural work, #10 or thicker.
- Flat head (countersunk) sits flush. Use this for visible surfaces or where clearance matters.
- Washer head distributes load over a wider area — right for metal roofing, deck frames, and any soft material that could pull through.
- Pilot holes are not always needed in dimensional lumber or softwood. For hardwood, pre-drilling prevents splitting on end grain.
Coatings
Outdoor structural work needs coated or stainless screws. Standard zinc-plated screws will corrode and snap within a few years in treated lumber or wet climates. Hot-dip galvanized is acceptable for most treated lumber; stainless is the safe choice near the coast or in constant moisture.
Where to buy
Compare current pricing across major suppliers — prices vary by region and season.
Related tools
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