A lot size is the minimum number of shares in an Options contract. The NSE F&O or Futures & Options lot size differs from index to index and stock to stock. For example, the lot size for Nifty 50 is 75 while that for Bank Nifty is 40. Similarly, the lot size for Reliance Industries is 1000 and that for TCS is 250. The lot size is decided by the exchanges BSE and NSE. From time to time, as required, these exchanges revise the lot size of indexes and stocks.