"Fortunately, Steem already provides a simple approximation known as the virtual STEEM supply which is calculated by adding up the total vesting STEEM, liquid STEEM, and the STEEM that would exist if all Steem Dollars (SBD) were to be instantly converted to STEEM. This metric multiplied by the current price of STEEM will produce a “market capitalization” or “enterprise value” that is closer to the true value of STEEM."
http://steemit.com/steem/@dantheman/how-to-calculate-the-market-capitalization-of-steem