Wood Screw Pilot Hole Size Calculator
Find the correct pilot hole drill bit size for any wood screw.
Prevents splitting, ensures proper grip, and gives the right size for hardwood and softwood.
A pilot hole is a small hole drilled before driving a screw. It serves three important purposes:
- Prevents the wood from splitting, especially near edges or ends of a board.
- Makes driving the screw easier — less torque required.
- Ensures the screw threads grip the wood properly for maximum holding strength.
The correct pilot hole size depends on the screw gauge (diameter), the type of wood (hardwood vs. softwood), and whether the hole is in the top piece (clearance hole) or the receiving piece (pilot hole).
For softwood (pine, spruce, cedar, poplar): The pilot hole should be about 60–70% of the screw’s minor (root) diameter — the diameter at the base of the threads, not the thread tips.
For hardwood (oak, maple, cherry, walnut): The pilot hole should be closer to 80–90% of the minor diameter, because hardwood does not compress around the threads the way softwood does.
Common wood screw sizes and recommended pilot hole diameters:
| Screw # | Outer Dia | Softwood pilot | Hardwood pilot |
|---|---|---|---|
| #4 | 2.9 mm (7/64") | 2.0 mm (5/64") | 2.4 mm (3/32") |
| #6 | 3.5 mm (9/64") | 2.4 mm (3/32") | 2.8 mm (7/64") |
| #8 | 4.2 mm (5/32") | 3.0 mm (7/64") | 3.5 mm (9/64") |
| #10 | 4.8 mm (3/16") | 3.5 mm (9/64") | 4.0 mm (5/32") |
| #12 | 5.5 mm (7/32") | 4.0 mm (5/32") | 4.8 mm (3/16") |
| #14 | 6.4 mm (1/4") | 4.8 mm (3/16") | 5.5 mm (7/32") |
For the top (clearance) hole — the piece the screw passes through — the hole should be the same diameter as the outer screw diameter. This lets the screw slide freely and pull the two pieces together.
Always drill to the full screw length minus a few millimetres. A pilot hole that is too short is nearly as bad as none at all.