This is a fairly common question. However there is no rule of thumb that states if you wear a ring size X, the ideal diamond size is Y. In the end it is a matter of personal preference. We have customers who wear a ring size 8, but wear a ring with a 0.75ct center stone. We also have customers who wear a ring size 4, but wear a 3ct or larger center stone. We recommend downloading our actual Moissanite size chart for assistance in choosing the perfect size.