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Screw Size Chart
Quick answer: Wood screw diameter = 0.060″ + (0.013 × gauge). A #8 is 0.164″, a #10 is 0.190″. Pilot holes: match the screw’s root diameter in hardwood, go one size under in softwood.
Every wood screw gauge from #0 to #24 with its exact diameter, the clearance hole it needs, and the pilot hole for both hardwood and softwood — plus the machine screw sizes and thread pitches.
Wood screw size chart
Wood screws are sized by gauge. The gauge is not arbitrary — it follows a formula: diameter = 0.060″ + (0.013 × gauge). A #8 screw is 0.060 + 0.104 = 0.164″. Every row below is computed from that relation, not copied from another chart.
| Gauge | Diameter (in) | mm | Shank clearance | Pilot — softwood | Pilot — hardwood |
|---|---|---|---|---|---|
| #0 | 0.060 | 1.52 | 1/16 | 1/64 | 1/32 |
| #1 | 0.073 | 1.85 | 5/64 | 1/32 | 1/32 |
| #2 | 0.086 | 2.18 | 3/32 | 1/32 | 3/64 |
| #3 | 0.099 | 2.51 | 7/64 | 3/64 | 1/16 |
| #4 | 0.112 | 2.84 | 7/64 | 3/64 | 1/16 |
| #5 | 0.125 | 3.17 | 1/8 | 1/16 | 5/64 |
| #6 | 0.138 | 3.51 | 9/64 | 1/16 | 5/64 |
| #7 | 0.151 | 3.84 | 5/32 | 1/16 | 3/32 |
| #8 | 0.164 | 4.17 | 11/64 | 5/64 | 3/32 |
| #9 | 0.177 | 4.50 | 3/16 | 5/64 | 7/64 |
| #10 | 0.190 | 4.83 | 3/16 | 3/32 | 7/64 |
| #12 | 0.216 | 5.49 | 7/32 | 7/64 | 1/8 |
| #14 | 0.242 | 6.15 | 1/4 | 7/64 | 9/64 |
| #16 | 0.268 | 6.81 | 17/64 | 9/64 | 5/32 |
| #18 | 0.294 | 7.47 | 19/64 | 9/64 | 3/16 |
| #20 | 0.320 | 8.13 | 21/64 | 11/64 | 13/64 |
| #24 | 0.372 | 9.45 | 3/8 | 3/16 | 7/32 |
Pilot sizes target the screw’s root diameter in hardwood and slightly under in softwood. Oak, maple and other dense species take the hardwood column; pine, fir and cedar take the softwood one.
Machine screw and bolt sizes
Machine screws use the same gauge numbers below 1/4″, then switch to fractional inches. Each size comes in a coarse (UNC) and fine (UNF) thread.
| Size | Major diameter (in) | Coarse (UNC) | Fine (UNF) |
|---|---|---|---|
| #0 | 0.0600 | #0-80 | #0-80 |
| #1 | 0.0730 | #1-64 | #1-72 |
| #2 | 0.0860 | #2-56 | #2-64 |
| #3 | 0.0990 | #3-48 | #3-56 |
| #4 | 0.1120 | #4-40 | #4-48 |
| #5 | 0.1250 | #5-40 | #5-44 |
| #6 | 0.1380 | #6-32 | #6-40 |
| #8 | 0.1640 | #8-32 | #8-36 |
| #10 | 0.1900 | #10-24 | #10-32 |
| #12 | 0.2160 | #12-24 | #12-28 |
| 1/4 | 0.2500 | 1/4-20 | 1/4-28 |
| 5/16 | 0.3125 | 5/16-18 | 5/16-24 |
| 3/8 | 0.3750 | 3/8-16 | 3/8-24 |
| 7/16 | 0.4375 | 7/16-14 | 7/16-20 |
| 1/2 | 0.5000 | 1/2-13 | 1/2-20 |
| 5/8 | 0.6250 | 5/8-11 | 5/8-18 |
| 3/4 | 0.7500 | 3/4-10 | 3/4-16 |
| 1 | 1.0000 | 1-8 | 1-12 |
Screw length and how much should bite
The rule that matters: at least two thirds of the screw should end up in the receiving piece. Fastening 3/4″ stock to a stud means a 2″ screw — 3/4″ through the board leaves 1-1/4″ of bite. A 1-1/4″ screw only reaches half an inch in and will pull out under load.
| Joining | Screw length | Bite into receiving piece |
|---|---|---|
| 1/2″ to framing | 1-1/4″ | 3/4″ |
| 3/4″ to framing | 2″ | 1-1/4″ |
| 1″ to framing | 2-1/2″ | 1-1/2″ |
| Two 3/4″ boards face to face | 1-1/4″ | 1/2″ |
| Deck board to joist | 2-1/2″ to 3″ | 1-1/2″ to 2″ |
Head types and when each one earns its place
- Flat (countersunk) — sits flush or below the surface. Needs a countersink in hardwood or it will split the grain.
- Pan — sits proud, bears on the surface. The default for metal and for anything you may take apart.
- Bugle — drywall and deck screws. The curved underside self-countersinks in soft material without tearing the face.
- Washer / flange — spreads the load. Use where the material is soft or the hole is oversized.
Frequently asked questions
What size is a #8 wood screw?
0.164 inches (4.17 mm) at the major diameter. It takes a 11/64 in shank clearance hole, a 5/64 in pilot in softwood and a 3/32 in pilot in hardwood.
How do I know what gauge screw I have?
Measure the outside diameter of the threads with a caliper, then work backwards through the formula: gauge = (diameter − 0.060) ÷ 0.013. A screw measuring 0.190 in gives (0.190 − 0.060) ÷ 0.013 = 10, so it is a #10.
Do I need a pilot hole for wood screws?
In hardwood, always — the screw acts as a wedge and splits the grain without one. In softwood you can often skip it away from edges, but within about two inches of an end you should still drill. Two holes are ideal: a clearance hole through the top piece and a pilot in the piece underneath.
What is the difference between a #8 and a #10 screw?
0.026 inches of diameter — #8 is 0.164 in, #10 is 0.190 in. That is roughly 34% more cross-sectional area, so a #10 carries meaningfully more load, but it also needs a larger pilot and splits thin stock more readily.