How to calculating an mysql articles size in Kb

i am trouble a problem. I want to know how to calculating my inserted Articles size in KB. plz help me to find out.

$query = "INSERT INTO tbl_post(cat,titile,body,author,tags) VALUES('$cat','$titile','$body','$author','$tags')";

This is my query and this is my blog site query.And i want to know how is my site articles size in KB as like show .

$body

size in kb.