How to Convert Number Drill Sizes to Inches

Written by suman medda
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How to Convert Number Drill Sizes to Inches
Different drill bits produce holes of different diameters. (Keith Brofsky/Photodisc/Getty Images)

Drills are one of the most essential and versatile tools in building, carpentry and auto mechanics. Drills can be used for tightening screws, sanding wood or making holes. Different drill bits, which are attached to the front of the drill, allow for these different uses. The most common type of drill bit is the one used to drill holes. Hole drilling bits are labelled from 1 to 80 and A to Z, with the letters used for larger diameters. Each bit produces a different diameter hole.

Skill level:


  1. 1

    Navigate to a drill bit conversion chart (see Resources). Three are provided.

  2. 2

    Locate the label on the drill bit. The label is generally at the base of the bit, away from the side that carves the hole.

  3. 3

    Locate the bit label on the chart and find the drill bit diameter. The charts provide the diameters in fractional inches, decimal inches and decimal millimetres.

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