There are a number of contenders for the position of smallest cell in the human body, but here is what I have been able to uncover so far:

Human Sperm Cell – 5 x 3 micrometers. The flagellum is up to 50 micrometers long.

Human Granule Cell; a cell in the cerebellum, hippocampus, olfactory bulb (relays smell information to the brain) and the cerebral cortex – one source sites 10 micrometers; another sites 4-4.5 micrometers.

Red Blood Cell – a cell responsible for distributing oxygen in the body measures 4.5-8.5 micrometers. The red blood cell is, however incapable of reproduction as it lacks a nucleus. All of its energy is needed to bind oxygen to hemoglobin to keep all of our cells alive, so when it is generated in the bone marrow and released into circulation, it loses its nucleus.

Want to know what is the biggest cell in the human body?