How to choose size and number of bar used for column?

As per IS 456:2000 choosing the size and number of bars for a column:

1. Minimum clear cover of 40mm provided for the column, and if column size is less than 200mm then clear cover is 25mm provided.
2. Minimum 4nos of 12mm diameter bar is provided.
3. Minimum area of steel should be 0.8% Ag and the maximum area of steel should be 6% of Ag if not overlapping and for overlapping 4% of Ag.
4. Maximum spacing shall not be greater than 300mm for two longitudinal reinforcements.
5. Diameter of the stirrup is 1/4*16
6. And maximum spacing shall be 16D-, 300mm, or B whichever is minimum.