How Big is a Micron?

SEM Micrograph of Red Blood Cells, Which are About 5 microns in Diameter

A "micron" is an abbreviated term for "micrometer", or a millionth of a meter (1/1,000,000 meters). This is about .00004 inches. For Size comparison, a human red blood cell is about 5 microns across. A human hair is about 75 microns across (depending on the person). Bacteria can be between about .2 microns and 3 microns in size.