best size of procedure cache size?

here is my dbcc memusage output:

DBCC execution completed. If DBCC printed error messages, contact a user with System Administrator (SA) role.

Memory Usage:

                                   Meg.           2K Blks                Bytes

      Configured Memory:     14648.4375           7500000          15360000000

Non Dynamic Structures:         5.5655              2850              5835893

     Dynamic Structures:        70.4297             36060             73850880

           Cache Memory:     13352.4844           6836472          14001094656

      Proc Cache Memory:        85.1484             43596             89284608

          Unused Memory:      1133.9844            580600           1189068800

So if proc cache is too small? I can put used memory 1133M to proc cache. but as many suggested that proc cache should be 20% of total memory.

Not sure it should be 20% of max memory or Total named cache memory?