The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). Humans contain about 50 to 100 trillion cells. Most plant and animal cells are between 1 and 100 micron and therefore are visible only under the microscope.
Depending on the source, that figure varies from 50 to 100 trillion cells. This number can vary, since the cells are always dying off and then multiplying inside all the time.
Some sources told us that the average adult human body is made up of “50 million million” (50 trillion) cells, while others put the figure closer to 10 trillion. Science NetLinks, a resource for science teachers, stated that there are approximately “ten to the 14th power” (that’s 100 trillion) cells in the human body.
Keep in mind, all of these figures are just estimates. At this time, there really is no way to know the exact number of cells in a human body. Can you imagine trying to count them all? Plus, as one source pointed out, the number will vary from person to person, depending on their size. The number of cells in your own body is constantly changing, as cells die or are destroyed and new ones are formed. So even the number of cells in your own body is not static.