Find out the number of rows returned by refcursor?

What is the best way to find out the total number of rows returned by
an refcursor?  This would allow the client user to know the total
amount of rows as they are using FETCH FORWARD/BACKWARD.

For example let's say that an refcursor has 300 rows.  The user fetches
20 at a time.  I would like the user to know that there are 300
possible rows.


regards,
karen