A pilot hole is a small hole you drill before driving a screw or a larger bit. It guides the fastener, keeps your material from splitting, and makes screws far easier to drive straight. This guide covers what pilot holes are, how to size them, and a handy screw-size chart you can bookmark.
What Is a Pilot Hole?
A pilot hole is a pre-drilled hole slightly smaller than the screw’s threaded shaft. When you drive the screw, its threads bite into the wall of the hole instead of forcing the wood apart — which is exactly what prevents splitting near edges and ends. Pilot holes also stop the screw from wandering and reduce the effort (and stripped heads) that come from driving a screw into solid material.
Why You Should Always Drill a Pilot Hole
- Prevents splitting — essential in hardwoods, near edges, and in trim.
- Keeps screws straight and exactly where you want them.
- Reduces effort and protects screw heads from stripping.
- Improves holding power by letting the threads grip clean material.
Pilot Holes vs. Clearance Holes
These two are easy to mix up. A pilot hole is drilled smaller than the screw threads so they bite. A clearance hole is drilled the size of the screw’s shank so the screw slips through the top board and pulls it tight against the piece below. When joining two boards, you often drill a clearance hole in the top board and a pilot hole in the bottom one.
How to Choose the Right Pilot Hole Size
The goal is a hole about the diameter of the screw’s solid core — the shaft without its threads. As a rule of thumb:
- Softwood (pine, cedar, fir): use a bit roughly equal to the core, or slightly smaller, so the threads grip well.
- Hardwood (oak, maple, hardwoods): go slightly larger — dense wood needs a bigger pilot to avoid splitting.
When in doubt, hold the bit in front of the screw: you should see the threads on either side of the bit, but not the solid core. Always test on a scrap piece first for critical work.
Screw Pilot-Hole Size Chart
Here are typical pilot and clearance sizes for common wood screws. Use the smaller pilot in softwood and the larger in hardwood:
| Screw size | Pilot (softwood) | Pilot (hardwood) | Clearance hole |
|---|---|---|---|
| #6 | 1/16" | 5/64" | 9/64" |
| #8 | 5/64" | 3/32" | 11/64" |
| #10 | 3/32" | 7/64" | 3/16" |
| #12 | 7/64" | 1/8" | 7/32" |
| 1/4" | 5/32" | 3/16" | 1/4" |
Pilot Holes for Tapping Threads
“Pilot hole” also comes up in metalworking, where you drill a precise tap drill hole before cutting threads with a tap. For example, a 1/4"-20 tap uses a #7 drill bit. If you’re tapping threads, use the correct tap-drill size rather than a wood-screw pilot — you’ll find those on the drill bit size chart too.
How to Drill a Pilot Hole (Step by Step)
- Mark the spot and, in metal, add a center-punch dimple so the bit doesn’t wander.
- Pick the pilot bit using the chart above (or match it to the screw’s core).
- Set the depth — drill to the depth the screw will reach, using tape on the bit as a depth marker.
- Drill straight at a steady speed, then back the bit out to clear the chips.
- Countersink if you want the screw head flush, then drive the screw.
Common Pilot-Hole Mistakes
- Too small in hardwood — the wood still splits or the screw snaps.
- Too large — the threads can’t grip and the screw strips out.
- Too shallow — the screw bottoms out and splits or breaks.
- Skipping it near edges — the most common cause of split trim and boards.
Frequently Asked Questions
What size drill bit for a #8 screw pilot hole?
What size pilot hole for a #10 screw?
Do I need a pilot hole for every screw?
What’s the difference between a pilot hole and a countersink?
The Right Bits for Clean Pilot Holes
A sharp, correctly sized bit makes all the difference. Brad-point bits keep pilot holes exactly on-center in wood, while HSS twist bits handle general drilling and metal.
