EXCEL formula IF

Hello,
Can someone help me? I want a formula to show OK if the cell beside it have some value.
Example:

A1: to be filled with D.O number (will only available once the D.O is received)
B1: OK (if the D.O number is entered)

I have list of thousand item in 1 sheet, need to monitor the completion of each item. if they have the D.O number, then the process of the item is completed.

Let say the list have 100 no of item, only 10 have the D.O number, then the progress will be 10 over 100 (10%).

Anyone have any idea how to easily monitor the completion of item?
Thank you.