I have no idea. However, there are probably charts around here (or the www somewhere) stating the width of an average .40 carat asscher... and the diameter of a size 9 ring... and I guess you could do the math.
An eternity band with stones that size might be uncomfortable between the fingers.
This one from Leon Mege is pretty close. The size or price isn't mentioned but the stones are about .47 each. That will give you an idea of the proportions.