The calculation
Why the bit shape changes the reference
A straight bit makes a constant-diameter hole. A tapered bit makes a changing diameter and must be matched to the intended screw and drilling depth. Choosing a number from the wrong column can produce a different fit even when the screw gauge is correct.
For a #8 conventional wood screw in this reference, the hardwood straight-bit entry is 1/8 in. Changing to a tapered bit changes that entry to 11/64 in. These are published reference combinations, not competing measurements of the same hole geometry.
Pilot and clearance holes are not the same
The pilot prepares the receiving piece for the threads. A clearance hole in the first piece allows the screw to pull that piece against the receiving piece. A countersink shapes the surface for a suitable screw head. One diameter does not perform all three jobs.
This tool returns only the pilot reference. It does not infer a clearance diameter, countersink angle, embedment depth, edge distance or load capacity.
Use the screw maker’s instructions first
Modern construction, deck and structural screws may have different roots, tips and drilling requirements from conventional wood screws. Manufacturer instructions take priority over this generic reference. Wood species, moisture, grain direction and proximity to an edge can also change the practical result.
Test a joint in matching scrap, inspect for splitting and confirm that the screw pulls the pieces together without stripping. The reference does not certify a connection for a particular load.
Questions from the workbench
Why do other charts show different sizes?
They may assume another screw design, root diameter, wood condition, bit shape or drilling method. Check those assumptions rather than averaging conflicting numbers.
Should I use this for pocket holes?
No. Pocket-hole jigs use their own stepped bits and setup instructions. Use the pocket-hole reference and your exact jig manual.
Sources and reference scope
Reference data checked November 7, 2026. Reference pilot sizes from Bolt Depot. Straight and tapered entries are separate; the tool does not infer one from the other.
See how we calculate and validate results. All entries are processed in your browser; the calculator does not upload or save them.