Prokaryotic cells vary in size, but they are typically much smaller than eukaryotic cells. The average prokaryotic cell is about 1-10 micrometers (µm) in length and 0.5-2 µm in width. In comparison, the average eukaryotic cell is about 10-100 µm in length and 10-100 µm in width.

Some of the largest prokaryotic cells are found in the bacterial genus Epulopiscium, which can reach lengths of up to 750 µm. The smallest prokaryotic cells are found in the archaeal genus Nanoarchaeum, which can be as small as 0.1 µm in diameter.