What does Excel LEN Function do? Excel LEN Function is to measure length of a text. Why do you need Excel LEN Function? Excel LEN Function is not quite meaningful to use alone, it is more of a stepping stone to achieve another purpose. LEN Function is most commonly used with the following functions in order to extract a substring from a string. LEFT Function - extract a substring on the left RIGHT Function - extract a substring on the right MID Function - extract a substring in the m...