Of each of the shapes that bacteria may appear in you will find different sizes as well.
A coccus bacteria, which will be cocci when adding plural numbers of bacteria, are round bacteria. These round, spherical or even oval bacteria can divide within a plane into two types of arrangement which are the diplococcus arrangement or the streptococcus arrangement. The diplococcus arrangement is an arrangement where the cocci will be arranged in pairs. The streptococcus arrangement is an arrangement that finds the cocci in chains. A coccus will typically be from 0.5 to 1.0 micrometers for its diameter which is one half to one millionth of a meter. These bacteria can further divide and multiply across more than one plane to form either tetrads which are square, sarcinas which are cubed, or, irregular clusters.
Bacteria that are rod like in appearance, the bacilli, measure 0.5 to 1.0 micrometers in breadth and 1.0 to 4.0 micrometers in length. Bacilli can single cell, arranged in chains to form streptobacillus or oval to form a coccobacillus. The third most common form that bacteria may appear in are spirals and these can be quite long when compared to the cocci or the bacilli. Spiral bacteria measure from 1.0 micrometers to over 100.0 micrometers in length. You may like to know that the spiral bacteria may be curbed or comma shaped which is when they are referred to as vibrio, they may be thick and rigid, these are called spirillum or they may be thin and flexible. Thin, flexible spirals go by the name spirochete.
There are even more bacteria to consider here. The trichome-forming, a large bacteria several micrometers longer than they are wide with widths measuring 2.0 to 4.0 micrometers. The stalked bacteria can range from 30.0 to 100.0 micrometers in diameter. Star-shaped bacteria, filamentous bacteria, lobed bacteria and bacteria sporting irregular shapes most commonly fall into a size range of approximately 1.0 micrometers in diameter yet unusual bacteria do exist with larger dimensions.
Giant bacteria, giant when compared to the other bacteria. They are the Epulopiscium fishelsoni which has a bacillus shape and measures 80 micrometers in diameter while the length of the organism can measure from 200 to 600 micrometers, and, the Thiomargarita namibiensis, a coccus that measures from 100 to 750 micrometers in diameter. These bacteria can sometimes be seen by the naked eye when in their largest sizes.
Square bacteria may be 2.5 micrometers across but are always only about 0.2 micrometers thick. Square bacteria are called archaea. Most recently some scientists believe they have uncovered a micro bacteria no more that 0.2 micrometers in diameter. This was reported by the University of California at Berkeley in 2006 in the month of December during shotgun cloning research.