A regular hexagon, 12 centimeters on a side, is inscribed in a circle.  What is the diameter of the circle in centimeters?

 

 

A regular hexagon will form 6 equilateral triangles.  Two sides of opposite triangles will form a diameter of the circle.  In the diagram,  is such a segment.

 

 

 

If each side of the hexagon is 12 centimeters,  is  centimeters.