The laws of chatzitzah, obstruction/separation, concerning washing our hands and immersing in a mikvah (ensuring the water touches our hands or body without a chatzitzah), applies only to something which fits tightly on the body. Something which is loose is not considered a chatzitzah, such as a woman’s ring if it is loose. Nevertheless, the custom is that women always remove their rings before ritually washing their hands, since we are not sufficiently knowledgeable in the precise halachic definition of what is loose or tight.
One of the suggested definitions of "loose" regarding a ring is if she were to shake her hand vigorously the ring would fall off. Yet, in order to be on the safe side, one should not immerse in a mikvah or wash hands for bread even with a loose ring, due to the concern it may halachically be considered tight even if it seems loose. Also, aside from not being able to determine the definition of loose versus tight, as a general principle le’chatchila, preferably, one should be stringent and not immerse with an item on the body even if it’s not considered a chatzitzah halachically.
Rav Yosef Yeshaya Braun, Badatz of Crown Heights, One Minute Halachah, #147, reprinted from crownheightsconnect.com