I don't think there is a limitation on the size of columns, as this is controlled by many factors, like:

1- Concrete clear cover to the reinforcement (ties) > 38 mm,

2- Clear spacing between main bars, which should be more than;

    i. 40 mm,

   ii. 1.5 bar diameter,

 iii.  4/3 Max. Aggregate size.

3- Least dimension of the column should be equal to or greater than 16 main bar                diameter.

4- Least dimension of the column should be equal to or greater than 48 tie diameter.

5- Least dimension of the column should be equal to or greater than the tie spacing.

6- Strength requirements.

All these are are indirect limitations.

There is a limitation on C1/C2 , that  minimum amount is 3 . Where C1 and C2 are dimensions of column .

I don't think there is a limitation on the size of columns, as this is controlled by many factors, like:

1- Concrete clear cover to the reinforcement (ties) > 38 mm,

2- Clear spacing between main bars, which should be more than;

    i. 40 mm,

   ii. 1.5 bar diameter,

 iii.  4/3 Max. Aggregate size.

3- Least dimension of the column should be equal to or greater than 16 main bar                diameter.

4- Least dimension of the column should be equal to or greater than 48 tie diameter.

5- Least dimension of the column should be equal to or greater than the tie spacing.

6- Strength requirements.

All these are are indirect limitations.

what about fire rating ?

Agree with Saad Altaan ...

should not less that 9"x9"

In ACI318 code, explicit minimum sizes for columns are not specifed to permit the use of reinforced concrete columns with small cross sections in lightly loaded structures, such as low-rise residential and light offce buildings. If small cross sections are used, there is a greater need for careful workmanship, and shrinkage stresses have increased signifcance .@ Hossam El-Agamy

Agreed with Saad Altaan sir

no need to comment after comments of saad altaan