Pilot Hole Chart for Wood Screws
It is usually good practice to bore the pilot hole the same size as the Root Diameter in hardwoods, and about 15% smaller in softwoods. See this chart for root diameter information.
| Size | Hard Woods | Soft Woods | ||
|---|---|---|---|---|
| Taper | Straight | Taper | Straight | |
| #2 | 3/32" | 1/16" | 5/64" | 1/16" |
| #3 | 7/64" | 5/64" | 3/32" | 1/16" |
| #4 | 7/64" | 5/64" | 3/32" | 1/16" |
| #5 | 1/8" | 3/32" | 7/64" | 5/64" |
| #6 | 9/64" | 7/64" | 1/8" | 3/32" |
| #7 | 5/32" | 7/64" | 9/64" | 3/32" |
| #8 | 11/64" | 1/8" | 5/32" | 7/64" |
| #9 | 3/16" | 9/64" | 11/64" | 1/8" |
| #10 | 13/64" | 9/64" | 3/16" | 1/8" |
| #12 | 7/32" | 5/32" | 13/64" | 9/64" |
| #14 | 1/4" | 11/64" | 15/64" | 5/32" |
| #16 | 9/32" | 3/16" | 17/64" | 11/64" |
| #18 | 5/16" | 7/32" | 19/64" | 13/64" |