According to Parenting, human eggs, or ova, measure in at 100 microns, or one-tenth of a millimeter, the same diameter as a strand of human hair. As Wikipedia points out, human egg cells are typically large enough to see with the naked eye, without the use of a microscope.
Parenting explains that the human egg cell is the largest cell in the human body. Sperm cells, on the other hand, are the smallest cells in the human body. Close up, an ovum looks like a sphere surrounded by a "halo," or corona.
According to Wikipedia, in mammals, the ova are fertilized inside the female's body. When the egg and sperm join inside the body, they create a zygote.