The thickness of hair can vary greatly depending on the species. Human hair can be as thin as 80 microns in diameter, while the hair of elephants and giraffes is over 350 microns in diameter.
It's important to note that hair thickness is not the same as hair density. Hair density refers to the number of hair strands per square inch of scalp. You can have fine hair but a high density, or thick hair but a low density.
While you can't increase the actual thickness of your hair, there are ways to make it appear thicker. This includes using hair care products that add volume, getting regular trims, and eating a healthy diet.