The cremation occurs in a crematory, consisting of one or more cremator furnaces or cremation retorts for the ashes. A cremator is an industrial furnace capable of generating temperatures of 870–980°C (1600–1800°F) to ensure disintegration of the corpse. A crematorium may be part of chapel or a funeral home, or part of an independent facility or a service offered by a cemetery.
Modern cremator fuels include natural gas and propane. Modern cremators have adjustable control systems that monitor the furnace during cremation.
A cremation furnace is not designed to cremate more than one body at a time, something that is illegal.
The chamber where the body is placed is called the retort. It is lined with refractory bricks that resist the heat. The bricks are typically replaced every five years because of thermal fatigue.
Modern cremators are computer-controlled to ensure legal and safe use; e.g., the door cannot be opened until the cremator has reached operating temperature. The coffin is inserted (charged) into the retort as quickly as possible to avoid heat loss through the top-opening door. The coffin may be on a charger (motorised trolley) that can quickly insert the coffin, or one that can tilt and tip the coffin into the cremator.
Some crematoria allow relatives to view the charging. This is sometimes done for religious reasons, such as in traditional Hindu and Jain funerals.
Most cremators are a standard size. Typically, larger cities have access to an oversize cremator that can handle deceased in the 200 kilograms (440 lb)+ range. Most large crematoriums have a small cremator installed for the cremation of fetal and infant remains.
Remains with large pieces are put into a machine, the "cremulator," that grinds them down to finer bone fragments that somewhat resemble wood-ash in appearance, but of higher density.
All that remains after cremation are dry bone fragments (mostly calcium phosphates and minor minerals). Their color is usually light grey. They represent very roughly 3.5% of the body's original mass (2.5% in children). Because the weight of dry bone fragments is so closely connected to skeletal mass, their weight varies greatly from person to person, although it is more closely connected with the person's height and sex than with their simple weight. The mean weight of adult cremated remains in a Florida, U.S. sample was 5.3 lb (approx. 2.4 kg) for adults (range 2 to 8 lb or 0.91 to 3.6 kg). This was found to be distributed bimodally according to sex, with the mean being 6 pounds (2.7 kg) for men (range 4 to 8 lb or 1.8 to 3.6 kg) and 4 pounds (1.8 kg) for women (range 2 to 6 lb or 0.91 to 2.7 kg). In this sample, generally all adult cremated remains over 6 pounds (2.7 kg) were from males, and those under 4 pounds (1.8 kg) were from females.
Jewelry, such as wristwatches and rings, are ordinarily removed and returned to the family. The only nonnatural item required to be removed is a pacemaker, because it could explode and damage the cremator. Also the mercury contained in a pacemaker's batteries poses an unacceptable risk of air pollution. In the United Kingdom, and possibly other countries, the undertaker is required to remove pacemakers prior to delivering the body to the crematorium, and sign a declaration stating that any pacemaker has been removed.