[resolutebat]

It's inherited from Japan, where 180ml is one gō, the standard measure for a portion of rice.

Even more confusingly, this originates from a Chinese unit which was standardized differently in modern China.

https://en.wikipedia.org/wiki/Ge_(unit)

[Modified3019]

Interesting. I wish they had just labelled it as a "gō" then, alongside the mL equivalent, and told us about why/the history in a blurb on the box/manual and then it'd have own neat little cultural thing going on.

[mdhen]

Rice cookers are all the same, they come with plastic measuring cups that are that size. I just call them rice cups.