Sharepoint - Maximum characters in Multiple lines of text Column

Document libraries and lists have different options available with respect to the multiple lines of text column type.

In document libraries, when you create a new column of type Multiple Lines of Text, you get the option to select the Allow unlimited length in document libraries checkbox.

But, In lists, this option does not exist.

A multi line text field is defined in SharePoint as a Note type, this is stored in the DB as a ntext sql type. In this SQL type you can store 2gb of char data, that's 1,073,741,823 characters.

Note: It is not advisable to store such huge data in SharePoint column as it may hamper performance.

Explanation referred from this TechNet

Also if your are working with multi lines text field in Doc libs then this is a nice article to read

I hope this is a helpful information!!

A Multiple lines of text column can store up to 63,999 characters