What is the RAM Size of iPad Mini ?

No one knows and we won't until someone does a teardown.

The RAM sizes are 16GB, 32GB, and 64GB.

See http://www.apple.com/ipad/compare/

16 or 32 or 64 GBs

Those are the flash memory sizes not RAM.

That is the flash storage size, I believe the OP is inquiring as to the onboard RAM.

The tech specs of the iPad mini are here

http://www.apple.com/ipad-mini/specs/

Unfortunately the RAM spec is not provided.

Corrections noted ... I thought you were asking about flash memory capacities.

According to this article:

http://www.heraldnews.com/cb_technicallyspeaking/x534153523/iPad-Mini-Microsoft- Surface-coming-out-this-week

it has half a gig (512MB) of RAM. This is the same as the iPad 2 (see http://en.wikipedia.org/wiki/IPad), superior to the iPad and inferior to the new iPad.