Bacteria are (extremely) small living things. While we measure our own sizes in inches or centimeters, bacterial size is measured in (microns). One micron is a thousandth of a millimeter: a pinhead is about a millimeter across. (Rod-shaped) bacteria are usually from two to four microns long, while rounded ones are generally one micron in (diameter). Thus if you enlarged a rounded bacterium a thousand times, it would be just about the size of a pinhead. An adult human (magnified) by the same amount would be over a mile (1.6 kilometer)tall.
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