The cun was part of a larger system, and represented one-tenth of a chi ("Chinese foot"). In time the lengths were standardized, although to different values in different jurisdictions. (See chi (unit) for details).
In Hong Kong, using the traditional standard, it measures ~3.715cm (~1.463in) and is called a "tsun". In the twentieth century in the Republic of China, the lengths were standardized to fit with the metric system, and in current usage in People's Republic of China and Taiwan it measures 31⁄3cm (~1.312in).
In Japan, the corresponding unit, sun(寸,sun), was standardized at 1000⁄33mm (~3.030cm, ~1.193in, or ~0.09942ft).