Buffer Cache Hit Ratio

SQL> column hit_ratio format 990.99
SQL> select (1-(sum(decode(name,'physical reads',value,0)) /
     (sum(decode(name,'db block gets',value,0)) +
     sum(decode(name,'consistent gets',value,0))))) as hit_ratio
     from v$sysstat;

HIT_RATIO
---------
     0.88