The industry standard size for an adult cremation urn is 200 cubic inches. This number is reached by figuring that, for every 1 lbs of human body weight, 1 cubic inch of space is needed for cremated remains. Thus, a 180 lbs adult will require an urn with the capacity to hold 180 cubic inches of cremains.
The formula is not perfect; usually, 180 lbs will translate to slightly less than 180 cubic inches, but it is a good rule of thumb to calculate. In the cremation process, body fat is completely incinerated while most of what remains is bone matter, so a larger individual will often require an urn of less than equal capacity to their actual weight.
When searching for a funeral urn, it is still best to follow the rule of 1 lbs equals 1 cubic inch, so here we have provided a selection of cremation urns that may suit your needs.