Wood Screw Pilot Hole Chart
A pilot hole is the small hole drilled before driving a wood or lag screw. It prevents splitting, reduces driving torque and decides how well the screw holds. Below: the full chart for #4–#14 wood screws and 1/4"–1/2" lag screws, with separate softwood and hardwood columns.
Wood screw pilot hole chart (#4 – #14)
Pilot for the threaded section; clearance for the unthreaded shank near the head:
| Screw gauge | Shank Ø | Pilot (softwood) | Pilot (hardwood) | Clearance hole |
|---|---|---|---|---|
| #4 | 0.112" | 3/64" | 7/64" | 1/8" |
| #5 | 0.125" | 1/16" | 1/8" | 9/64" |
| #6 | 0.138" | 1/16" | 9/64" | 5/32" |
| #7 | 0.151" | 5/64" | 5/32" | 11/64" |
| #8 | 0.164" | 3/32" | 11/64" | 3/16" |
| #9 | 0.177" | 3/32" | 3/16" | 13/64" |
| #10 | 0.190" | 1/8" | 3/16" | 7/32" |
| #12 | 0.216" | 9/64" | 7/32" | 1/4" |
| #14 | 0.242" | 5/32" | 1/4" | 17/64" |
Lag screw / lag bolt pilot hole chart
Lag screws are large wood screws with a hex head — "lag bolt" is the common trade name. Drill the pilot into the receiving piece; for long lags, drill deeper in steps:
| Lag size | Pilot (softwood) | Pilot (hardwood) |
|---|---|---|
| 1/4" | 5/32" | 3/16" |
| 5/16" | 3/16" | 7/32" |
| 3/8" | 7/32" | 1/4" |
| 1/2" | 5/16" | 11/32" |
A 3/8 in lag screw takes a 7/32 in pilot in softwood and 1/4 in in hardwood; a 5/16 in takes 3/16 in and 7/32 in. For hardwood, waxing the threads cuts driving torque nearly in half.
Why the pilot size matters
holding power = wood fibers compressed around the thread pilot too small → screw stalls, head snaps, wood splits pilot too big → threads strip, screw spins, no grip softwood: pilot ≈ 70% of shank · hardwood: pilot ≈ 90% of root Ø
The same #8 screw that snaps in oak without a pilot drives easily with an 11/64 in hole. The compression the pilot leaves is what grips the screw — that is why the hardwood column is always the larger bit.
Frequently asked questions
What size pilot hole for a #8 wood screw?
For a #8 wood screw, drill 3/32 in in softwood and 11/64 in in hardwood. The clearance hole for the unthreaded shank is 3/16 in.
What size pilot hole for a 3/8 lag screw?
Drill 7/32 in in softwood and 1/4 in in hardwood for a 3/8 in lag screw. The pilot matches roughly 40–60% of the shank diameter.
What happens if the pilot hole is too small?
In hardwood the screw stalls or the head snaps off; in softwood the wood can split near the edge. When in doubt, step up one bit size.
Do self-tapping screws need a pilot hole?
Metal self-tapping screws need a correctly sized pilot hole to cut their thread cleanly — see the tapped-hole guide. Wood screws always need one in hardwood.