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?