Columns need to be supported by a footing. In some cases this can be the same footings that support your foundation walls, but more often or not they will be placed on their own separate footing, also know as a pad. For columns these pads usually are square.
To calculate the volume for a column plus pad you need the diameter and height of the column plus the length of one of the sides and depth of the pad.
Formula used for Column and Pad Volume:(( (PI*diam/2*height)+( length*width*depth))*#