What Is GD&T?

Geometric Dimensioning and Tolerancing (GD&T) is a symbolic language used on mechanical drawings to communicate design requirements. Engineering, manufacturing, and inspection personnel must all be fluent in this system to make it effective. But it’s not as simple as just learning the symbols. GD&T can also be thought of as a design philosophy that integrates the function of the part into the tolerances.

Below is a sample GD&T drawing:


This engineering system is based on the Y14.5 standard (ASME Y14.5-2018) in North America. In other countries, prints often use the ISO series of tolerancing standards, which is similar to the ASME standard.