It is me or It is I

"It is I" is grammatically correct, though many English speakers don't know this any more and use "It's me"

The rule of using the nominative after the verb to be came into English because it is the Latin rule, as I understand it....

"I" is correct.

"Is" is a linking verb, so you want the predicate nominative "I", not the object "me".

(However, this is one of those things people tend to screw up so often that you'll hear "It's only me" far more frequently. In the United States, you may even seem pretentious if you say "It is I!")

Thank you so much