Query on X$BH table

Hi,

I want to find how many DB blocks are cached and used and how many are left unused. I use the query:

select state,count(*) from x$bh group by state;

and U get:

STATE COUNT(*)
---------- ----------
0 24
1 9972
3 4

Does this mean that 24 blocks were never used? 4 awereused but are available...

Some people say this is not the right query...So how do I query the x$bh?

Thanx!