Is this a question about congenital hemangiomas (RICH or NICH) versus the more "typical" hemangioma?
The congenital hemangiomas do not grow after birth. If you mean that the "typical" hemangioma was in some way visible at birth, I don't think that is an indication of how much it will grow.
My youngest had two hemangiomas. The one on the cheek was visible at birth and was a nickel sized bunch of blue/purple blood vessels. We didn't notice the other one, on top of the head, until she was several days (or maybe a week) old. Of course, maybe it was there and we just didn't notice.
The one on the cheek was much larger than the one on top of the head. By two months, the cheek hemangioma was about 2 inches in diameter, protruded an inch from the face, but the other was only an inch in diameter, protruded a half-inch.
In any case, I don't think there is a good way of telling how large the hemangioma will become. I do think, however, if the hemangioma has not shown very rapid growth by the time the child is 3 or 4 months old, it is unlikely to become very large.