UCDavis uses following MIB Objects:
memTotalReal
memCached
memBuffer
memAvailReal
Spectrum 10.3.2 and CAPC 3.7
The formula is as follows:
((memTotalReal-(memCached + memBuffered + memAvailReal)) * 100)/memTotalReal
For example:
((196573560-(10782268 + 277564 + 2228200)) * 100)/196573560
Would be 93%