Pilot Hole Calculator

Find the right drill bit for a wood screw before you drive it — the pilot hole equals roughly the screw root diameter so threads grip without splitting the wood.

How It Works

Pilot holes are sized to the screw root (minor) diameter. The softwood bit is slightly smaller than the screw, and the hardwood bit slightly larger, because dense grain splits more easily. Clearance (through) holes are drilled in the top board only, and the countersink matches the head diameter for a flush finish.

Reference values only — always confirm critical fastening decisions against your engineering specification or the fastener manufacturer.

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