How to Select Drill Bit Sizes

Updated February 21, 2017

Drill bit sizing is important. When drilling for wood screw placement, the drill bit must be slightly larger than the shank of the screw. If the hole is too small, the screw can crack the wood. Too big, and it weakens the screw function. The drill bit should be approximately the same size as the screw threads. Take a few minutes and select the correct size bit for the job.

Place a screw inside the jaws of an adjustable wrench. Close the jaws slightly until they touch both sides of the screw threads.

Take the screw out of the jaws. Insert drill bits between the jaws until you find one that fits as tightly as the screw did.

Place the bit into the drill. Drill a hole in a test piece of wood.

Insert the screw into the hole. Push and pull it up and down. It should fit snugly, but should not get stuck in the hole.

Check the length of the screw. If it's more than 3 inches long, you'll need an extra long bit.


Use the same method to find the correct bit size for larger bolts.

Things You'll Need

  • Adjustable wrench
  • Drill bit assortment
  • Cordless drill
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Specializing in hardwood furniture, trim carpentry, cabinets, home improvement and architectural millwork, Wade Shaddy has worked in homebuilding since 1972. Shaddy has also worked as a newspaper reporter and writer, and as a contributing writer for Bicycling Magazine. Shaddy began publishing in various magazines in 1992, and published a novel, “Dark Canyon,” in 2008.