Pilot Hole Size Chart

A pilot hole sized correctly for softwood will split hardwood, and one sized for hardwood leaves noticeably less thread engagement — and therefore less holding power — than softwood actually needs, which is why this chart runs two columns instead of one and why picking the wrong column is a common, avoidable mistake.

The chart, in drill-bit-friendly fractions

Gauge	Softwood pilot	Hardwood pilot
4	1/16" (0.0625)	5/64" (0.078125)
6	5/64" (0.078125)	3/32" (0.09375)
8	3/32" (0.09375)	7/64" (0.109375)
10	7/64" (0.109375)	1/8" (0.125)
12	1/8" (0.125)	9/64" (0.140625)

Every hardwood pilot in this table is exactly one drill-bit fraction step (1/64") larger than the corresponding softwood pilot — a consistent, easy-to-remember pattern once you notice it, even though the underlying reason (hardwood's denser fiber structure resists a driven screw's wedging action far more than softwood's) isn't itself a clean, linear relationship.

Why the gap exists

A screw doesn't cut a hole through wood the way a drill bit does — it wedges its way in, displacing and compressing fiber around the threads as it drives. Softwood fiber compresses relatively easily, so a smaller pilot hole (leaving more wood for the threads to grip) still allows the screw to drive without splitting the surrounding material. Hardwood fiber resists that same compression far more, which means a pilot hole sized for softwood concentrates enough wedging force in hardwood to split the board — usually visible as a crack running along the grain away from the screw, sometimes not visible until the piece is stressed later. The larger hardwood pilot relieves that wedging pressure at the cost of slightly less thread engagement, which is the trade this whole chart represents.

When to size toward the larger end of a range

Species vary in density even within the "hardwood" and "softwood" categories this chart uses as its two columns — a dense hardwood like hard maple or hickory benefits from a pilot hole toward the larger end of the hardwood column, while a lighter hardwood like poplar or basswood can often get away with something closer to the softwood figure despite technically being a hardwood botanically. When working near the end grain of any species, or near the edge of a board where there's less surrounding material to resist a split, size up regardless of species — end-grain and near-edge driving are the two situations most likely to split even with an otherwise-correct pilot hole.

MDF and particleboard need their own judgment call

Neither column in this chart was built for engineered sheet goods, which have no long grain to split along but also grip a screw thread far more weakly than either softwood or hardwood per unit of thread engagement — see /reference/hardboard-and-particleboard-sizes/ for why. In practice, sizing toward the hardwood end of this chart (or slightly larger) is the safer default for MDF specifically, prioritizing not stripping the surrounding material over maximizing thread engagement, since MDF's failure mode under an undersized pilot is crumbling around the hole rather than a clean split.

Depth matters as much as diameter

A pilot hole drilled to the correct diameter but too shallow still risks splitting, because the screw's unthreaded shank and tip continue wedging past the bottom of the hole once the bit-drilled portion runs out. Drill the pilot at least as deep as the screw will penetrate, not just deep enough to start the thread — and see /reference/screw-length-selection-by-joint-thickness/ for how deep that penetration should actually go for a given joint thickness in the first place, since pilot depth is only useful once you know the target screw length.

A two-step pilot for the clearance side

The board the screw head sits against (the "clearance" piece, as opposed to the "anchor" piece the threads bite into) generally needs a larger hole than either column in this chart — one close to or slightly over the screw's shank diameter, so the screw pulls the two pieces together instead of threading into both and jacking them apart. This is a genuinely separate drilling operation from the pilot hole covered above, and skipping it is one of the more common reasons a screwed joint doesn't close up tight even when the pilot hole in the anchor piece was sized correctly. A combination bit that drills the clearance hole, a countersink, and the pilot hole in one pass handles both operations without needing to switch bits mid-joint.

Reading a drill index instead of memorizing fractions

Most fractional drill bit sets sold for shop use step in 1/64" increments across this exact range, so a numbered or lettered index isn't strictly necessary for wood screw pilot holes the way it is for machine-screw tapping — but if your bit set only comes in more common 1/32" increments, round toward the nearer larger size in hardwood and the nearer smaller size in softwood, since the consequence of a slightly-too-large softwood pilot (a bit less thread grip) is milder than the consequence of a slightly-too-small hardwood pilot (a split board).