Please Note: In most instances, the average adult, when cremated, will produce around 200 cubic inches of ashes. When shopping for an urn, this will be the most prevalent size you find sometimes it will hold a little more or a little less, but this is the average adult size. Children younger than 13 depending on their height and size will yield roughly 100-122 cubic inches when cremated. Children under the age of 8, as well as infants, yield roughly 50 cubic inches after cremation.