There's more...

First, in order to turn this calculation into a measure, simply replace the first line of the CountOfItems calculation with the following:

VAR __List = MAX('R03_Table'[List])

Second, this recipe can work with any delimiter between values. Simply replace the middle parameter of the SUBSTITUTE function with the delimiter used within your list.

Third, you may run into a situation where you have a multi-character delimiter such as the following table, R03_Table1, where the delimiter is a double quote followed by a comma followed by a space followed by another double quote:

List

"One, Two"

"One, Two", "One, Two"

"One, Two", "One, Two", "One Two Three"

"One, Two", "One, Two", "One Two Three", "One, Two, Three"

 

In this circumstance, the same recipe can be used with minor modifications as follows:

CountOfItems = 
    VAR __List = 'R03_Table1'[List]
    VAR __Length = LEN( __List )
    VAR __Delimiter = """, """
    VAR __LenDelimiter = LEN(__Delimiter)
    VAR __Length2 = LEN( SUBSTITUTE( __List , __Delimiter , "" ) )
    VAR __Count = DIVIDE(__Length - __Length2 , __LenDelimiter, 1)
RETURN
    __Count + 1