Hello,

The size of the columns depends on the total load on the columns. There are axial loads and lateral loads. Large beam spans induce bending moment not only in the beams, but also in columns. For determining the size of the column in G+1 , G+2 or any place in a building, the basic criteria is load acting on that particular column. Actual loads are taken and the size is worked out.

However, minimum size of an RCC column should not be less than 9" x 12" (225mm x 300mm) with 4 bars of 12 MM Fe415 Steel.

Hope this is helpful.
Thank you.