You need to choose the size of column suitable for your project by making a layout on paper. As shown in the example below, for hexagon columns only, the outside width of the column flats or the face length equals the radius.
Our 30” diameter cocktail table had a 7” wide column with flats measuring 3 1/2”. To make a layout on paper draw a straight line. On the center point of this line draw a circle with a compass using a radius of 3 1/2”. Where the straight line meets the circle use the compass with the same radius to mark the next intersection. Continue walking around the circle until complete. Join these six equal marks. This is the size of your finished column.