Use a drill bit conversion chart to convert various drill bit sizes between different numbering systems. For example, the drill bit conversion chart on CSGNetwork.com is a table of drill bits in fractions of inches, those fractions as decimals, the drill wire gauge, and the metric equivalent in millimeters. With this table, users can easily see what size a drill bit measured in imperial units would be in metric units.
A common use of drill bit conversion charts is to compare the drill wire gauge to a measurement in inches or millimeters. Drill wire gauge is a commonly used system for identifying drill bits and is expressed as either a number or letter. Wire gauge one is between 7/32 and 15/64 of a inch. Larger bits are identified with letters (larger bits have later letters alphabetically) and smaller bits are identified with numbers (smaller bits have higher numbers).
In the United States, both fractional inch and wire gauge drill bit sizes are common. However, outside of the United States, nearly every country uses metric bit sizes.
Some drill bit conversion charts facilitate creating holes with female screw threads. The typical method of creating such holes is to drill a hole and then use a tap to create the female screw threading. In this instance, the appropriately-sized drill bit is called the tap drill.