Pilot Hole Size Chart: What Drill Bit for Every Screw
Drilling the right pilot hole size is the difference between a screw that drives smoothly and one that splits the wood or strips the thread. Too small and the wood splits. Too large and the screw has nothing to grip. The drill bit you reach for is the pilot hole size — same question, two names for it. Here is the complete reference.
Quick answer: Size the pilot to the thread’s root diameter — the solid core under the threads, not the shank and not the outside of the threads. Always pilot-drill in hardwood and near board edges. Use a larger clearance hole through the top piece so the screw clamps rather than lifts it.
| Screw | Softwood Pilot | Hardwood Pilot | Clearance Hole |
|---|---|---|---|
| #6 | 5/64" | 3/32" | 9/64" |
| #8 | 7/64" | 1/8" | 11/64" |
| #10 | 9/64" | 9/64" | 3/16" |
| #12 | 5/32" | 11/64" | 7/32" |
↓ Full charts for every gauge, metric, sheet metal, and lag screws below.
How deep should a pilot hole be?
At least as deep as the threads that will sit in the lower piece, and a little deeper does no harm. Stopping short is what snaps screws — the tip bottoms out and the head keeps turning. For lag screws, drill the pilot the full length of the threaded section.
What size pilot hole for a 1/4" lag screw?
5/32" in softwood, 3/16" in hardwood, with a full 1/4" clearance hole through the piece being fastened. Drill the pilot to the full thread length — a half-depth pilot is how lag screws shear off.
What is a clearance hole?
A hole through the top piece wide enough that the screw’s threads pass through without biting. It lets the head pull the two pieces together. Skip it and the screw threads into both pieces at once, holding them apart instead of clamping them — the gap you sometimes see under a screw head.
Pilot Hole Size Chart — Wood Screws
Quick answer: for a #8 wood screw, drill a 7/64" pilot hole in softwood or 1/8" in hardwood. Full chart for every gauge below.
| Screw Gauge | Shank Dia. | Softwood Pilot | Hardwood Pilot | Clearance Hole | Countersink |
|---|---|---|---|---|---|
| #4 | 0.112" | 3/64" | 1/16" | 1/8" | 0.225" (7/32") |
| #6 | 0.138" | 5/64" | 3/32" | 9/64" | 0.279" (9/32") |
| #8 | 0.164" | 7/64" | 1/8" | 11/64" | 0.332" (21/64") |
| #9 | 0.177" | 7/64" | 9/64" | 3/16" | 0.358" (23/64") |
| #10 | 0.190" | 9/64" | 9/64" | 3/16" | 0.385" (25/64") |
| #12 | 0.216" | 5/32" | 11/64" | 7/32" | 0.438" (7/16") |
| #14 | 0.242" | 11/64" | 3/16" | 1/4" | 0.507" (1/2") |
About the countersink column: these are head diameters from ASME B18.6.1 — a countersink is cut to the width of the screw head, so that is the number you are aiming for. The fractions look unfamiliar because countersink bits are not sold in those sizes; they are sold by gauge. Buy the #8 countersink for a #8 screw and the geometry is already right. The decimals matter when you are cutting a countersink with a straight bit or checking an existing hole.
Pilot sizing is a convention, not a standard. The charts on this page size softwood pilots to roughly 85% of the thread’s root diameter and hardwood pilots to the root diameter itself — the common trade convention, and the one that balances grip against splitting.
The American Wood Council publishes tighter figures — around 70% of root diameter in softwood and 90% in hardwood — optimised purely for withdrawal strength. Those grip harder, but they split more readily near board ends and edges, and they are much harder to drive by hand. Other published charts go the other way and use the full root diameter in softwood. If a chart you are comparing against differs from this one by a drill size, that is almost always why.
What Size Drill Bit for a #8 Screw?
A #8 wood screw takes a 7/64" drill bit in softwood and a 1/8" bit in hardwood. If the screw has to pass through a top board into a second piece, that top board gets an 11/64" clearance hole instead, so the head can pull the joint closed.
#8 is worth calling out on its own because it is the default gauge for cabinet work, furniture, deck boards and most general construction — if a project does not specify a gauge, it is usually a #8.
Why other charts give you a different number
Look this up in three places and you will get three answers, anywhere from 5/64" to 11/64". Some of that is genuine disagreement over how tight a pilot should be. But part of it looks like something simpler that nobody states outright: straight bits and tapered bits are not named for the same measurement.
A straight twist bit is named for the hole it cuts: a 7/64" bit cuts a 7/64" hole all the way down. A tapered bit cannot work that way, because the hole it leaves is wide at the surface and narrow at the tip. Here is the part worth noticing: DeWalt lists the #8 bit in its DW2535 tapered set as 11/64", which is the same as the #8 clearance hole in the chart above — and a #8 shank measures 0.164" against 11/64" at 0.172". That points to the tapered bit being named for its widest point rather than for the pilot it actually leaves at the tip.
If that reading is right, a chart quoting 11/64" for a #8 and a chart quoting 7/64" are describing two different bits, not contradicting each other. Either way, the practical fix is the same: check which kind of bit a chart means before you use its number. Every figure on this page is a straight-bit size — the ones that match the twist bits in an ordinary index.
| #8 Screw — What You Are Drilling | Bit Size | Why |
|---|---|---|
| Pilot, softwood | 7/64" | Just under the root diameter so threads still bite |
| Pilot, hardwood | 1/8" | Dense grain splits, so the hole matches the root |
| Clearance, top board | 11/64" | Threads pass freely so the head clamps the joint |
| Tapered combo bit | 11/64" | Sold as 11/64" — appears to be its widest point |
Pilot Hole vs Clearance Hole vs Countersink — What Each Does
- Pilot hole: Drilled in the receiving piece (the piece the screw grips). Sized smaller than the screw thread so threads cut into the wood. Prevents splitting.
- Clearance hole: Drilled in the top piece (the piece being fastened). Sized larger than the screw shank so the screw slides through freely. Allows the screw to clamp the two pieces together — without it, the screw lifts the top piece instead of clamping it.
- Countersink: Angled recess that allows a flat-head screw to sit flush with the surface. Match countersink angle to screw head angle (82 degrees for most standard screws).
The clearance hole is what closes the joint. Without it the threads grip both boards and the screw holds them apart instead of pulling them together.
Sizes verified against manufacturer fastener specs.
When Do You Need a Pilot Hole?
- Always in hardwood (oak, maple, ipe, cumaru) — hardwood will split without a pilot hole regardless of screw size
- Within 1 inch of any edge in softwood or plywood — edge grain splits easily
- For screws #10 and larger in softwood — large screws split softwood near edges
- Not required for small screws (#6 and under) in the middle of softwood panels
Metric Pilot Hole Chart
| Screw Size | Softwood Pilot | Hardwood Pilot | Clearance Hole |
|---|---|---|---|
| M3 | 1.5 mm | 2.0 mm | 3.5 mm |
| M4 | 2.0 mm | 2.5 mm | 4.5 mm |
| M5 | 2.5 mm | 3.5 mm | 5.5 mm |
| M6 | 3.0 mm | 4.0 mm | 6.5 mm |
| M8 | 4.0 mm | 5.5 mm | 9.0 mm |
| M10 | 5.0 mm | 7.0 mm | 11.0 mm |
Sheet Metal Screw Pilot Hole Chart
Self-tapping sheet metal screws still need a pilot hole in metal — the "self-tapping" part refers to cutting threads, not drilling through steel. Size the pilot to the screw’s root diameter, and go slightly larger in thicker or harder stock so the screw doesn’t snap.
| Screw Size | Thin Steel (up to 18 ga) | Thick Steel (14 ga and heavier) |
|---|---|---|
| #6 | 7/64" | 1/8" |
| #8 | 1/8" | 9/64" |
| #10 | 9/64" | 5/32" |
| #12 | 5/32" | 3/16" |
| 1/4" | 3/16" | 7/32" |
For self-drilling (Tek) screws with a drill point, no pilot is needed in steel up to the point’s rated thickness — see the Tek screw guide for point ratings.
Lag Screw Pilot Hole Chart
Lag screws — also called lag bolts, or coach screws outside North America — need two holes: a clearance hole through the piece being fastened, sized to the shank diameter, and a pilot hole in the receiving wood, sized to the root diameter of the threads. Skip the pilot hole in hardwood and the screw will shear off; oversize it and you lose most of the withdrawal strength.
| Lag Screw Size | Clearance Hole (top piece) | Pilot — Softwood | Pilot — Hardwood |
|---|---|---|---|
| 1/4" | 1/4" | 5/32" | 3/16" |
| 5/16" | 5/16" | 3/16" | 7/32" |
| 3/8" | 3/8" | 7/32" | 1/4" |
| 1/2" | 1/2" | 5/16" | 3/8" |
Drill the pilot to the full thread length. For structural connections, consider structural screws instead of lag bolts — no pilot hole needed and full code approval.
Amazon's ChoiceScrew Gauge Sizes Compared: #6 vs #8 vs #10 vs #12
Screw gauge numbers are not fractions and they are not millimetres — they are just positions on a scale. A bigger number is a thicker screw, and the steps are even: every gauge adds 0.013" of diameter.
That makes the whole system one line of arithmetic:
Shank diameter = 0.060" + (0.013" × gauge)
A #8: 0.060 + (0.013 × 8) = 0.164". A #12: 0.060 + (0.013 × 12) = 0.216". It holds exactly for every gauge in ASME B18.6.1.
| Gauge | Shank Diameter | Nearest Fraction | Where It Shows Up |
|---|---|---|---|
| #4 | 0.112" | 7/64" | Small trim, hinges on light doors |
| #6 | 0.138" | 9/64" | Cabinet hardware, thin stock |
| #8 | 0.164" | 5/32" | The default. Cabinets, furniture, decking |
| #9 | 0.177" | 11/64" | Common in deck screws only |
| #10 | 0.190" | 3/16" | Heavier framing, hinges, hardware |
| #12 | 0.216" | 7/32" | Structural connections, ledgers |
| #14 | 0.242" | 1/4" | Heaviest wood screw before lag territory |
Is a #14 screw the same as a 1/4" screw?
No, and the gap matters. A #14 measures 0.242". A 1/4" screw measures 0.250". They are 0.008" apart — close enough that the two get used interchangeably in conversation, far enough apart that a hole drilled for one is wrong for the other. #14 is the largest standard wood screw gauge; above it you are into lag screws, which are sized in fractions rather than gauges.
#10 vs #12: which should you use?
A #12 is 0.026" thicker than a #10 — about 14% more shank diameter, and meaningfully more holding power in the same length. Use a #10 for general hardware, hinges and mid-weight framing; step up to a #12 where the joint carries real load, such as a ledger, a post base or a heavy gate hinge. The pilot hole moves with it: 9/64" for a #10 in either wood, 5/32" softwood and 11/64" hardwood for a #12.
Pilot Holes in Hardwoods That Split (Oak, Maple, Ipe)
Dense hardwoods punish undersized pilot holes: the wood can’t compress around the threads, so it either splits along the grain or shears the screw head off. Three adjustments for oak, hard maple, hickory, and tropical decking like ipe: go up one bit size from the softwood column (or use the hardwood column religiously), always countersink so the head isn’t wedging the surface fibers apart, and drill the pilot to full screw depth — a half-depth pilot in ipe is how screws snap flush with the surface. A swipe of paste wax or bar soap on the threads cuts driving torque noticeably in the densest species.
Countersink bit sets and brad-point drill bit sets are available at Home Depot, Lowe's, and RONA across Canada and the US, as well as on Amazon. The brand-name sets above (DeWalt, Milwaukee, Bosch, Makita) are all stocked at major tool retailers.
Recommended Countersink Bit Sets
A combo countersink bit drills the pilot hole, clears the shank, and countersinks the head in one pass — the fastest way through a repetitive screw layout. All four below use a 1/4" hex shank and fit any drill; what separates them is which gauges they cover and whether the pilot bits are replaceable when they dull.
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Tapered vs Straight Bits
A straight twist bit drills a uniform-diameter hole — fine for most pilot holes, and what the charts above assume. A tapered pilot bit matches the natural taper of a traditional wood screw's shank, cutting a wider hole near the surface and narrower at the tip in one pass; some tapered bits include a matching countersink collar so pilot, clearance, and countersink happen together. Tapered bits shine with old-style slotted or Phillips wood screws that have a pronounced taper — modern sharp-point construction screws (most deck and cabinet screws today) are straight-shanked, so a straight bit is the simpler, equally effective choice for them.
Quick Reference: The Sizes You'll Use Most
Every number below is repeated from the charts above — this is the one to screenshot.
| Fastener | Softwood Pilot | Hardwood Pilot | Clearance Hole |
|---|---|---|---|
| #6 wood screw | 5/64" | 3/32" | 9/64" |
| #8 wood screw | 7/64" | 1/8" | 11/64" |
| #10 wood screw | 9/64" | 9/64" | 3/16" |
| #12 wood screw | 5/32" | 11/64" | 7/32" |
| 1/4" lag screw | 5/32" | 3/16" | 1/4" |
| 3/8" lag screw | 7/32" | 1/4" | 3/8" |
| M6 screw | 3.0 mm | 4.0 mm | 6.5 mm |
Sheet metal screws use their own sizes — see the sheet metal chart. Full gauge-by-gauge tables are at the top of this page.
Not sure which screw gauge you need?
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Frequently Asked Questions
Do I always need a pilot hole for wood screws?
No. Softwoods like pine and spruce usually take #6–#8 screws without a pilot, especially with modern sharp-point screws. You always need one in hardwood, near board ends and edges (within about 2 inches), for screws #10 and larger, and for brass or other soft-metal screws that snap easily.
What happens if the pilot hole is too big?
The threads have nothing to bite — holding power drops fast and the screw strips or pulls out under load. If you’ve overdrilled, move up one screw gauge, use a longer screw to reach fresh wood, or fill the hole with a glued hardwood plug or toothpicks and re-drill.
Can I use a regular twist bit for pilot holes?
Yes — standard twist bits work fine in wood. Brad-point bits are better (they don’t wander off your mark and leave cleaner entry holes), and combination countersink bits drill the pilot, clearance, and countersink in one pass, which is worth it for repetitive work.
What size pilot hole for a #10 screw?
9/64" in softwood, 9/64" in hardwood, with a 3/16" clearance hole through the piece being fastened.
Do deck screws need pilot holes?
In pressure-treated lumber, usually not — most deck screws are designed to self-drill in softwood. You do need pilots within 2 inches of board ends to stop splitting, and always in hardwood decking like ipe. See the deck screw guide for sizing.
What size drill bit for a #6 screw?
5/64" in softwood and 3/32" in hardwood, with a 9/64" clearance hole through the top piece. #6 is the usual gauge for cabinet hardware, drawer slides and thinner stock.
What size drill bit for a #12 screw?
5/32" in softwood and 11/64" in hardwood, with a 7/32" clearance hole. #12 is a structural size — ledger boards, post bases and heavy gate hinges — and always needs a pilot, in any species.
What size countersink bit for a #8 screw?
Buy a #8 countersink rather than a fraction. Countersink bits are sold by screw gauge, and a #8 is already ground to the right 82-degree angle and width. The recess it cuts measures 0.332" across, matching the head diameter given in ASME B18.6.1.
Related Guides
- Wood Screw Size Chart — Complete gauge to diameter reference
- Deck Screws Complete Guide — Outdoor screw selection
- Drill Bit Size for Concrete Anchors — Anchor pilot holes
- Drill Bit Selector — Instant bit recommendation for any material
- Screw Size Selector — Get your exact screw spec instantly
- Nail Size Chart: Penny Sizing Explained — Common vs sinker vs box nail diameters, and the real IRC requirements
- Bolt and Wrench Size Chart — SAE and metric wrench sizes, plus torque and thread pitch
