Drill Bit Sizes Chart

Three separate systems size drill bits sold in the US: fractional (1/16" through 1", in 1/64" steps), number (#1 through #80), and letter (A through Z). If you are buying your first set, start with fractional. It covers the widest range of everyday jobs, and the fractions stamped on the shank match what a tape measure already shows.

This page is a buying guide: which sizes to get first, how to tell the three systems apart, and where the decimal value of a size actually matters. For the exhaustive fractional, letter, and number reference tables, see the full drill size chart.

Fractional bits handle most general drilling: pilot holes, dowel joinery, hardware clearance, and anything you would otherwise measure with a tape. A 29-piece fractional set (1/16" to 1/2" in 1/64" steps) covers the overwhelming majority of home and shop jobs.

Number bits fill in the small end. Anything smaller than 1/16", and most machine-screw tap drills, land on a number size rather than a clean fraction. If you tap threads for machine screws (like a 6-32 or 8-32 screw), you need a number set to hit the correct pilot hole.

Letter bits fill the gap between fractional 1/4" and 1/2". Several common tap drill sizes, including the tap drill for a 1/2"-13 bolt, land on a letter size instead of a clean fraction or number. Buy a letter set only once you find yourself needing one of those specific in-between sizes.

If you are building a starter set rather than buying a full 29-piece case, these ten fractional sizes cover the large majority of general hardware, wood screw, and hobby work:

Most fractional bits stamp the fraction directly on the shank near the shank end, such as "1/4" or "3/8". Number and letter bits stamp the number or letter instead, such as "#7" or "F". When the stamp has worn off or was never legible, measure the bit's diameter with a caliper and match the decimal reading to the closest row in the drill size chart, the letter drill chart, or the number drill chart.

The size numbers are identical across materials since they describe the hole diameter, not what you are cutting. What changes is the bit's material and tip geometry. General-purpose high-speed steel (HSS) handles wood, plastic, and soft metal. Cobalt bits hold an edge longer in stainless steel and hardened metal. Carbide-tipped or solid-carbide bits cut masonry, tile, and abrasive material that would dull an HSS edge quickly. Buying the right size bit in the wrong material is one of the most common reasons a "correct size" bit still produces a rough or oversized hole.