Pilot Hole & Clearance Hole Size Calculator
Find the pilot hole, clearance hole, and countersink size for any wood screw gauge, before you drill.
Wood hardness:
Pilot & Clearance Hole Sizes by Screw Gauge
| Gauge | Hardwood pilot | Softwood pilot | Clearance hole | Countersink dia |
|---|---|---|---|---|
| 0 | 3/64 (No.58) | 1/32 (No.69) | 1/16 (No.52) | 1/8 |
| 1 | 3/64 (No.55) | 1/32 (No.65) | 5/64 (No.47) | 3/16 |
| 2 | 1/16 (No.53) | 3/64 (No.59) | 3/32 (No.42) | 3/16 |
| 3 | 1/16 (No.51) | 3/64 (No.56) | 7/64 (No.37) | 1/4 |
| 4 | 5/64 (No.48) | 3/64 (No.55) | 7/64 (No.32) | 1/4 |
| 5 | 5/64 (No.44) | 1/16 (No.53) | 1/8 (No.30) | 1/4 |
| 6 | 3/32 (No.42) | 1/16 (No.52) | 9/64 (No.27) | 3/8 |
| 7 | 3/32 (No.38) | 1/16 (No.50) | 5/32 (No.22) | 3/8 |
| 8 | 7/64 (No.35) | 5/64 (No.48) | 11/64 (No.18) | 3/8 |
| 9 | 1/8 (No.32) | 5/64 (No.46) | 3/16 (No.14) | 3/8 |
| 10 | 1/8 (No.30) | 3/32 (No.44) | 3/16 (No.10) | 1/2 |
| 11 | 1/8 (No.29) | 3/32 (No.43) | 13/64 (No.4) | 1/2 |
| 12 | 9/64 (No.27) | 3/32 (No.39) | 7/32 (No.2) | 1/2 |
| 14 | 5/32 (No.20) | 7/64 (No.34) | 1/4 (D) | 1/2 |
| 16 | 3/16 (No.16) | 1/8 (No.31) | 17/64 (I) | 5/8 |
| 18 | 3/16 (No.10) | 9/64 (No.29) | 19/64 (N) | 5/8 |
| 20 | 7/32 (No.3) | 5/32 (No.26) | 21/64 (P) | 3/4 |
| 24 | 1/4 (No.D) | 11/64 (No.18) | 3/8 (V) | 3/4 |
Source: engineeringtoolbox.com, "US Wood Screws - Pilot Holes"
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Why Pilot Hole Size Matters
A pilot hole lets the screw's threads bite into wood fiber without splitting it. Too small, and driving a screw into hardwood can split the piece outright or snap the screw head off under the torque. Too large, and the threads have nothing to grip — the screw spins freely or holds weak.
Hardwood and softwood need different pilot sizes for the same screw. Hardwood fiber resists splitting less than softwood fiber resists stripping, so hardwood pilots run slightly larger than softwood pilots for the same gauge — the table above reflects that difference at every size.
Pilot hole and clearance hole solve different problems. The pilot hole goes into the piece the screw's threads will grip. The clearance hole goes through the piece being fastened on top — sized so the screw shank slides through without threading, so clamping force pulls the two pieces together instead of just threading into both.
A countersink widens the top of the clearance hole so a flat or oval screw head sits flush with (or just below) the surface, instead of standing proud. Match the countersink diameter to the screw head diameter, not the shank — an undersized countersink leaves the head sitting high.
See also: Wood Shrinkage Calculator · Board Foot Calculator