Cremation is the practice of disposing of a human corpse by burning which often takes place in a crematorium or crematory. Along with burial, cremation is an increasingly popular alternative for the final disposition of the dead.

The place where the cremation takes place is called a 'crematorium'. A crematorium consists of one or more furnaces called 'cremators' (often mistakenly called 'ovens') and facilities for handling of the ashes. A cremator is an industrial furnace capable of reaching high temperatures up to approximately 870-980 °C (1600-1800 °F) with special modifications to ensure the efficient disintegration of the corpse. One of these modifications is the aiming of the flames at the torso, where a majority of the body's mass rests.

A crematorium may be part of chapel or a funeral home, or it may be part of an independent facility or a service offered by a cemetery.

The body burns in the cremator.The cremators use a number of different fuel sources, such as natural or propane gas. Prior to this coal or coke was often used by crematoriums up to the early 1960s. Modern cremators include control systems which monitor the conditions inside the furnace while a cremation is taking place. The operator can make adjustments to provide for more efficient burning, as well as ensuring that minimal environmental pollution occurs.

A cremation furnace is not designed to cremate more than one body at a time, and to do so is illegal in many nations including the USA.

The chamber where the body is placed is called the retort. It is lined with special refractory bricks to help retain the heat. These bricks require replacement after about five years because of continual expansion and contraction due to temperature cycling.

Modern cremators are computer-controlled with safety devices and interlocks to ensure legal and safe use, e.g., the door cannot be opened until the cremator has reached the correct operating temperature. The coffin is inserted (charged) into the retort as quickly as possible to avoid heat loss from the top-opening door. The coffin may be on a motorised trolley (known as a charger) which can insert the coffin at speed, or one that can tilt to tip the coffin down a slope into the cremator.

Crematoriums will allow relatives to view the charging and sometimes this is done for religious reasons, e.g., Hindus. However, notwithstanding the respect with which the deceased is treated, this is fundamentally an industrial process, and not recommended for the sensitive or faint-of-heart.

Cremators are a standard size. Large cities will have access to an oversize cremator that can handle deceased in the 200+ kg range. However, the morbidly obese cannot always be accommodated and must be buried instead. Most large crematoriums have a small cremator installed for the disposal of fetal remains, babies and infants.

A body to be cremated is first placed in a container for cremation, which can be a simple corrugated cardboard box or a wooden casket. Most casket manufacturers provide a line of caskets specially built for cremation. Another option is a cardboard box that fits inside a wooden shell designed to look like a traditional casket. After the funeral service the interior box is removed from the shell before cremation, permitting the shell to be reused.

Funeral homes may also offer rental caskets, which are traditional caskets used only for the duration of the services, after which the body is transferred to another container for cremation. Rental caskets are sometimes designed with removable beds and liners, replaced after each use.

In Australia, the deceased is cremated in a coffin supplied by the undertaker. Reusable or cardboard coffins are unknown. If cost is an issue, a plain, particle-board coffin known in the trade as a 'chippie' will be offered. Handles (if fitted) are plastic and approved for use in a cremator. Coffins vary from unfinished particle board (covered with a velvet pall if there is a service) to solid timber. Most are veneered particle board.

Cremations can be 'delivery only' with no preceding chapel service at the crematorium (although a church service may have been held) or preceded by a service in one of the crematorium chapels. Delivery-only allows crematoriums to schedule cremations to make best use of the cremators, perhaps by holding the body overnight in a refrigerator. As a result a lower fee is applicable. Delivery-only may be referred to by industry jargon such as 'west chapel service'.

The box containing the body is placed in the retort and incinerated at a temperature of 760 to 1150 °C (1400 to 2100 °F). During the cremation process, a large part of the body (especially the organs) and other soft tissue is vaporized and oxidized due to the heat, and the gases are discharged through the exhaust system. The entire process usually takes about two hours.

All that remains after cremation are dry bone fragments (mostly calcium phosphates and minor minerals). These representing roughly 3.5% of the body's original mass (2.5% in children, but these figures vary greatly due to body composition). Because the weight of dry bone fragments are so closely connected to skeletal mass, their weight varies greatly from person to person, with the mean weight in a Florida, U.S. sample being 5.3 lbs (approx. 2.4 kg) for adults (range 2 to 8 lbs/900 g to 3.6 kg). This is distributed bimodally, with the mean being 6 lbs (2.7 kg) for men (range 4 to 8 lbs/1.8 kg to 3.6 kg) and 4 lbs (1.8 kg) for women (range 2 to 6 lbs/900 g to 2.7 kg). In this sample, generally all adult cremated remains over 6 lb (2.7 kg) were from males, and those under 4 lb (1.8 kg) were from females.

Jewelry, such as wristwatches and rings, is ordinarily removed and returned to the family. The only non-natural item required to be removed is a pacemaker, as a pacemaker could explode and damage the cremator. 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.

After the incineration is completed, the bone fragments are swept out of the retort, and the operator uses a pulverizer called a cremulator[3] (also known informally as a crembola[citation needed]) to process them into what are known as cremains which exhibit the appearance of grains of sand (note that this varies with the efficiency of the cremulator used, and recognizable chips of very dry bone may be seen in some final product cremated remains, depending on origin and facility). Cremulators usually use some kind of rotating or grinding mechanism to powder the bones, such as the heavy metal bearings on older models.

In Japan and Taiwan, the bones are not pulverized unless requested beforehand, and are collected by the family.

This is one of the reasons cremated remains are called ashes although a technical term sometimes used is "cremains" (a portmanteau of "cremation" and "remains"). The ashes are placed in a container, which can be anything from a simple cardboard box to a fancy urn. An unavoidable consequence of cremation is that a tiny residue of bodily remains is left in the chamber after cremation and mixes with subsequent cremations.

Not all that remains is bone. There will be melted metal lumps from missed jewellery, casket furniture, and dental fillings, and surgical implants such as hip replacements. Large items such as titanium hip replacements are usually removed before grinding, as they may damage the grinder. After grinding, smaller bits of metal are sieved out and later interred in common, consecrated ground in a remote area of the cemetery.