Drill bit for screw size.
Drill bit for screw size: Find the right pilot, tap, or clearance drill for any screw size given the material.
The right pilot, tap, or clearance hole for any screw — adjusted for material. Softwood, hardwood, metal, and plastic all need different sizes.
How this works
Three different "drill for screw" questions get conflated in real life:
- Pilot hole — a hole that a self-tapping screw screws into. Sized smaller than the screw so the threads bite, but big enough that the wood doesn't split. Used for wood screws and sheet-metal screws.
- Tap drill — a hole that gets cut to threads with a tap. Sized to leave ~75% of the thread height when the tap cuts. Used for machine screws into solid material.
- Clearance hole — a hole the screw passes through freely. Sized slightly larger than the screw OD. Used in the top piece of a two-piece joint (the bottom piece gets the pilot or tap drill).
Material matters too. Softwood compresses; hardwood splits. A pilot hole that's perfect in pine will crack walnut. This calculator picks the right size given both pieces of information.
Common questions
What is the difference between a pilot hole and a clearance hole?
A pilot hole goes in the piece the screw threads into and is sized to the screw's root (minor) diameter so the threads bite. A clearance hole goes in the top piece the screw passes through and is slightly larger than the screw's outer diameter, so the shank slips through and lets the two pieces pull tightly together.
What size pilot hole do I need for a wood screw?
In softwood, use a pilot about 70% of the screw's outer diameter; in hardwood, about 90% (close to the root diameter) to prevent splitting. For example, a #8 screw (0.164 in) takes roughly a 3/32 in pilot in softwood and 7/64 in in hardwood.
Do self-tapping or drywall screws need a pilot hole?
Usually not — self-tapping screws into thin sheet metal and drywall screws into drywall cut their own hole. But in hardwood, near an edge or end, or in brittle material, a pilot still prevents splitting and lowers the driving torque.
Why is the drill size for metal different from wood?
Metal needs a precise tap drill (for threading) or clearance drill (for machine screws passing through), sized to exact fractions of the screw diameter. Wood fibers compress and grip, so wood pilots are smaller, percentage-based, and more forgiving.
What happens if the pilot hole is the wrong size?
Too large and the threads have nothing to grip, so the screw strips or pulls out. Too small and you risk splitting the material, snapping the screw, or camming out the head from excessive driving torque.
Should I countersink the hole?
For flat-head screws that must sit flush or below the surface, yes — countersink the clearance hole to match the head angle (82° for most inch flat-head screws). Otherwise the head wedges against the surface and can split the material or stand proud.
Sources
- Wood screw pilot holes: American Wood Council guidance; cross-checked with screw manufacturer (e.g., GRK, Spax) recommendations.
- Tap drills: Machinery's Handbook 31st ed., Table 3 — Tap Drill Sizes for 75% Thread.
- Clearance holes: ASME B18.2.8 — Clearance Holes for Bolts, Screws, and Studs.
Disclaimer. Recommended bit sizes are starting points. Wood density varies by species, grain orientation, and moisture content — what works in dry softwood may split when used on dense hardwood near a board edge. For critical or visible joints, test on scrap first. For threaded holes in metal, follow your tap manufacturer's specific drill recommendation when given.