PK Space calculation for table with composite key as PK

[Virinchi T]

Hi



I am trying to understand what is the correct way to calculate the Primary Key usage for a table in mysql 5.7



Imagine, I have table where primary is on two columns and each column have different datatype.



PRIMARY KEY ( 'column A','column B')



column A mediumint(5) unsigned
column B varchar(25)



In this case , what is correct way to calculate PK space usage for this table