The process of adding size information to a drawing is known as dimensioning, and standard dimensioning practices have been established for this purpose.

There are different standards for different types of drawings, such as architectural drawings, mechanical drawings, highway drawings, steel detail drawings, welding drawings, and so on. In this chapter, the focus will be on mechanical drawings.

The most common dimensioning standard used in the United States today was developed and is updated by the American National Standards Institute (ANSI) and is published by the American Society of Mechanical Engineers (ASME). The current version of this standard is ASME Y14.5. The dimensioning practices described in this text follow this latest ASME standard.