The human egg is the largest cell in the human body. And it’s a beautiful sight to behold: Under the microscope, the maturing egg cell is a sphere surrounded by a radiant corona. At a size of 100 microns, or one-tenth of a millimeter, that’s equivalent to the diameter of a single strand of hair. (Sperm cells, the other half of the reproductive equation, are much, much smaller.) In fact, sperm cells are the smallest cells in the human body.