How is the Market Cap calculated?
Market Cap is calculated by the current price timed by the current circulating supply.
The market cap of any coin is determined by the circulating supply of the coin times by the current price of the coin. Here is an example with Bitcoin.
16,825,000 x $11611 = $195355075000
As you can see the answer is Bitcoins current Market Cap. (25/01/2018)