A bacteria is a few microns, or a few micrometers in length. A micron or micrometer is 1 x 10
-6 meters in length.
E. coli is about 8 microns in length. Links are provided to relevant Wikipedia articles.
The smallest bacteria are of cocci: DIALISTER OR MICROCOCCUS 0.5 to 3.5 micrometer, and the largest bacteria is spirillum that is of 15-22 micrometer.