What size pilot hole for a #8 screw?
A #8 wood screw wants a 3/32" pilot in hardwood and 5/64" in softwood, with an 11/64" clearance hole through the top piece. Sizes for every gauge from #2 to #14.
A #8 screw wants a 3/32" pilot in hardwood and 5/64" in softwood.
Through the top piece — the one being pulled down — drill 11/64" so the threads pass without biting. That clearance hole is what makes the joint pull tight.
How that is worked out
- A pilot hole is sized to the screw's *root*, the solid core inside the threads, so the threads still have wood to cut into. It is not sized to the shank.
- Hardwood takes a larger pilot than softwood at the same gauge, because dense wood splits rather than compressing when a thread wedges into it.
- The top piece gets a clearance hole sized to the *outside* of the thread. Without it the screw threads hold both pieces apart and the joint never closes — the single most common reason a screwed joint has a gap in it.
Pilot and clearance drills by screw gauge
| Gauge | Pilot — hardwood | Pilot — softwood | Clearance (top piece) |
|---|---|---|---|
| #2 | 3/64" | 1/32" | 3/32" |
| #3 | 1/16" | 3/64" | 7/64" |
| #4 | 1/16" | 3/64" | 7/64" |
| #5 | 5/64" | 1/16" | 1/8" |
| #6 | 5/64" | 1/16" | 9/64" |
| #7 | 3/32" | 1/16" | 5/32" |
| #8 | 3/32" | 5/64" | 11/64" |
| #9 | 7/64" | 5/64" | 3/16" |
| #10 | 7/64" | 3/32" | 3/16" |
| #12 | 1/8" | 3/32" | 7/32" |
| #14 | 9/64" | 7/64" | 1/4" |
Worth knowing
- Drill the pilot as deep as the screw goes, not just through the surface. A screw bottoming out in a short pilot snaps its head off, and an extracted broken screw costs more time than the hole saved.
- Near an end or an edge, go up a size and wax the threads. End grain splits along the grain with very little provocation.
- Self-drilling deck and construction screws are designed to skip the pilot in softwood, and mostly do. In hardwood or near an edge they split it anyway — drill.
Work out your own numbers
- Pilot hole calculator
The right drill bit for a wood screw, by gauge number and by softwood or hardwood.
- Pocket hole screw calculator
Screw length and thread by material thickness, and how far apart to space the holes along an edge joint.
Related questions
- What is the difference between a pilot hole and a clearance hole?
- The pilot hole is in the bottom piece and is sized to the screw's root so the threads bite. The clearance hole is in the top piece and is sized so the threads pass through freely without biting at all. You want both: the threads pull against the bottom piece only, and that is what draws the joint closed. A screw threaded into both pieces jacks them apart instead.
- Do I need a pilot hole in plywood?
- In the face, usually not for anything up to about a #8. Into the edge of plywood you do, every time — the plies split apart along their glue lines and the damage is invisible until the joint fails. Use the hardwood size there, and keep well back from the corner.
- What size pilot hole for a #10 screw?
- 7/64" in hardwood, 3/32" in softwood, with a 3/16" clearance hole through the top piece. The whole table is above — the pattern is that the pilot grows roughly with the gauge, and hardwood runs one or two drill sizes up from softwood at the same gauge.