Which Cell Is the Largest in the Human Body?

Cell sizes in the human body span several orders of magnitude. The egg cell (ovum), at about 120 micrometres (0.12 mm) in diameter, is the largest by volume and the only human cell visible without a microscope — it is about the size of the period at the end of a sentence. The egg is large because it must contain nutrients and molecular machinery to support the first cell divisions after fertilisation before the embryo implants. The longest human cell is a motor neuron: its cell body sits in the spinal cord, but its axon extends down the leg to the foot — a single continuous cell over 1 metre long, yet only 10-20 micrometres wide. The smallest human cells are platelets (2-4 micrometres) and red blood cells (6-8 micrometres). Sperm cells, including their tails, are about 50 micrometres long but are mostly tail (flagellum) with a tiny head.