The Nifty Bank Index represent about 13.34% of the free float market capitalization of the stocks listed on NSE and 86.13% of the free float market capitalization of the stocks forming part of the Banking sector universe as on December 30, 2011
The above statement means for example if we consider the total free float market cap of all stocks listed on NSE is 100 then the sum of free float market cap of all stocks forming the Nifty Bank index is 13,34% of total listed on NSE. The market cap of total stocks forming the Nifty bank index covers 86.1% of all banking sector. To note one should understand only scrips which met some pre set criteria are eligible to enter in to that particular index.