Bacteria ka size kaafi chhota hota hai, aur yeh typically 0.2 to 2.0 micrometers (µm) ke range mein hota hai. Lekin kuch bacteria is range se bade ya chhote bhi ho sakte hain. Example ke taur par, *Escherichia coli* (E. coli) bacteria ka size lagbhag 1-2 µm hota hai.