Individual strands of hair range in thickness from 1/1500 to 1/500 of an inch in diameter, depending on the properties of the hair in question. Typically, blond hair is thinnest since it usually does not have a middle layer like dark hair does. Black hair is the coarsest or thickest.
Hair found on different parts of the body, even hairs found on the same person, can vary greatly in size as well as thickness. Temperatures and humidity also affect hair diameter. Warm air causes hair to get thicker. For these reasons, there is no widely accepted value or standard measurement for hair diameter.