"It is ME" is not grammatically correct in the academic sense, but is used in spoken English.
"
It is I" is grammatically correct in the pure sense, but would never be used in spoken English - or very rarely by people who speak in an ultra-formal dialect.
"It is I" would have been correct in Shakespeare's time, in spoken English, but not now.
english.stackexchange.com/users/4353/tegner
As reported from the NOAD: me /mi/ pronoun [first person singular] 1. used by a speaker to refer to himself or herself as the object of a verb or preposition:
Do you understand me?
Wait for me!
• used after the verb to be and after than or as :
Hi, it's me.
You have more than me.
•
informal to or for myself:
I've got me a job.
It's then correct to say
it's me .
english.stackexchange.com/users/252/kiamlaluno
The answer to the question 'Who's there?'
is 'It's me.' '
It is I' would normally be heard only when something else follows it, and then only in rather formal contexts, as in 'It is I who have done all the work, so it is I who should get the compensation.'
english.stackexchange.com/users/12952/Barrie England
"It is me," is more common, and correct.
However, "It is I who am here," is also correct, and "who am here" can be left off and implied, making "It is I," also correct.
english.stackexchange.com/users/10460/xpda
This question is related to I can run faster than...
In that exchange nohat describes the pronouns being used in the nominative and accusative cases.
Modern English speakers have become more comfortable using the accusative case in comparisons even though traditionally comparisons have used the nominative case.
It is further noted that "both forms are standard.
"
Modern English has slurred the distinction between cases, using word order to denote case rather than declension.
We still use different words for most personal pronouns (he/him, I/me, we/us), but have lost it for you/you.
"I talk to you."
"You talk to me."
When asking "Who is there?" it would be correct to answer in the nominative case, "I am here."
Likewise, asking "Who is it?" should elicit "
It is I" or "I am it."
english.stackexchange.com/users/3800/oosterwal
While it is formally correct to say "It's I", while informal or popular usage allows "It's me", it would be incorrect to say "It's him and I" (as in the title of a currently popular song), which mixes objective and nominative cases; it could be either "
It's he and I" or "It's him and me".
english.stackexchange.com/users/270974/Dustin G
I was taught at school that the following expression is not grammatically correct:   Who is there? It's me.   The correct one is:   Who is there? It's I.   Can you let me know which one is accurate?  Here is a good explanation about both forms.
Which one is correct to say: "It's me" or "It's I"?
english.stackexchange.com
<pronouns><grammatical-case><be><predicative-complement>
english.stackexchange.com/questions/10643
english.stackexchange.com/users/4319/Muaz Khan
It is generally considered that "It's me" or "It's I" are both standard forms. "It is ME" is not grammatically correct in the academic sense, but it is used in common speech. "It is I" would rarely be used in spoken English, and whilst it may have been correct in Shakespeare's time, it is no longer. "It is me" is not grammatically correct, but used in spoken English. "It is I" grammatically, would be the more correct form, but less used in modern English. "I" would normally be correct if something else followed the sentence, for example, If the answer was extended to "It is I who am here" this would also be correct, so it could be implied "It is I" is correct. Both forms are considered correct. Over time the lines have blurred in distinguishing nomnative from accusative cases.
It is generally considered that "It's me" or "It's I" are both standard forms. "It is ME" is not grammatically correct in the academic sense, but it is used in common speech. "It is I" would rarely be used in spoken English, and whilst it may have been correct in Shakespeare's time, it is no longer. "It is I" is technically correct, but would be considered overly formal in normal speech. "It is me" is more common.
While it is gramatically correct to say "It is I", while informal spoken usage is "It is me". "It is I" would have been correct in Shakespeare's time, in spoken English. "It is I" would normally be heard only when something else follows it and then only in rather formal contexts. "It is me" is what is commonly said and many people will consider it to be correct. However, "It is me" is technically grammatically incorrect, whilst "It is I" would be the grammatically incorrect phrase. Despite this, "It is I" is only likely to be heard in very formal circustances. It was used more often in the past, but is rarely used today.
In that the pronouns being used in the nominative and accusative cases.
In that the pronouns being used in the nominative and accusative cases.
 "It is ME" is not grammatically correct in the academic sense, but is used in  spoken  English.   Normally "I" would have something following it. Both forms standard. Distinction unclear.
"It is I" is technically correct, but would be considered overly formal in normal speech. "It is me" is more common.
"It is I" is grammatically correct and "It is me" is grammatically incorrect. "It is I" would have been correct long time ago but is no longer used. "It is I" will only today be heard in very formal contexts. "It is me" is more common and some people will consider it to be correct.