VMware has made available a tool which can help users who currently run vSphere 4 or Virtual Infrastructure 3.5. to calculate and determine their current vRAM usage and vRAM capacity as if they upgraded to vSphere 5.0.
The tool lets you connect to your current environment which it analyzes, based on that data the tool provides the vRAM capacity and usage for each vSphere 5.0 equivalent edition.
More information about the new licensing can be found in the whitepaper titled:"VMware vSphere 5.0 Licensing, Pricing and Packaging whitepaper"