The largest cell in the human body is the oocyte when size means the diameter or volume of a free, roughly spherical cell. The smallest intact human cell by volume is the sperm cell. The longest is a neuron, whose thin projection can run for more than one meter.
Those answers differ because a cell can be wide, voluminous, or long without leading all three measurements.
What is the largest cell in the human body?
The human oocyte is the largest free, roughly spherical cell in the body, with a mean diameter of about 115 micrometers when its surrounding coat is excluded.[1]
The 2022 study measured 1,563 immature oocytes and found diameters from 60 to 171 micrometers. The mean was 115 micrometers, and oocytes that completed maturation averaged 123 micrometers.[1] The human body contains trillions of cells, but few approach this width.
Treating a 115-micrometer oocyte as a sphere gives a volume of about 0.80 nanoliters. That is a ProteinIQ calculation from the study's mean diameter. It describes the cell inside the zona pellucida, not the extracellular coat or the surrounding cumulus cells.
“Largest by volume” still needs a boundary rule. A skeletal muscle fiber is a long, multinucleated syncytium formed by cell fusion, so including syncytia changes the comparison. The oocyte is the clearest answer for a single, unfused human cell.
What is the smallest cell in the human body?
The sperm cell is the conventional smallest intact human cell by volume: one study measured a mean volume of 17.4 cubic micrometers.[2]
Its head is also tiny. Reference measurements put the median sperm-head length at 4.1 micrometers and width at 2.8 micrometers.[3] The flagellum makes the whole cell much longer than its head, so sperm is not the shortest human cell from end to end.
Platelets are only about 2 to 3 micrometers across, but they are anucleate fragments shed by megakaryocytes rather than complete cell types produced by cell division.[4] If fragments count, a platelet can be narrower than a sperm head.
A spherical 115-micrometer oocyte has about 46,000 times the volume of a 17.4-cubic-micrometer sperm cell.[1][2] This ratio is calculated from the two reported measurements and should be read as an order-of-magnitude comparison because both cell populations vary.
What is the longest cell in the human body?
The longest cell in the human body is a neuron: the peripheral process of a sensory neuron running from the lower spine to the big toe can exceed one meter.[5]
Most of that distance is a narrow axon-like process, not the cell body. Human dorsal-root-ganglion cell bodies measured in culture were 28 to 56 micrometers in diameter, while some of their peripheral processes were only about one micrometer across.[5] A neuron can therefore be the longest human cell without being the widest or largest by volume.
This geometry also explains why a count of brain neurons says little about their combined length. Each neuron can branch, and the total length of those branches is different from the maximum straight-line span of one cell.
What are the largest and smallest cells in the world?
Across life, the smallest widely cited self-replicating cells are about 0.3 micrometers wide, while a single multinucleate cell can extend for meters. There is no single record until “cell” and “size” are defined.
Mycoplasma genitalium is the standard answer to “what is the smallest cell in the world?” Its diameter is about 0.3 micrometers, near the proposed lower size limit for an actively growing, self-replicating cell with DNA, ribosomes, and a membrane.[6] Viruses can be smaller, but they are not cells and cannot reproduce without entering a host cell.
At the other end, the green alga Caulerpa taxifolia is a coenocyte: one continuous cell with many nuclei and no internal cell membranes dividing its cytoplasm. Reported individuals reach 2.8 meters.[7] If the comparison is limited to bacteria, Thiomargarita magnifica has an average cell length above 9,000 micrometers, and the longest measured cells approach 20,000 micrometers, or 2 centimeters.[8]
The chart compares each example's longest reported dimension on a logarithmic scale. The slender neuron, filamentous bacterium, spherical oocyte, and branching coenocyte have very different shapes, so their volumes cannot be read from the bars. The plotted values come from the cited cell-size, sperm, oocyte, neuron, bacterium, and alga sources.[1][3][5][6][7][8][9]
The ostrich ovum is the usual animal-world answer to “what is the largest cell?” A cell-size review describes it as about 8 centimeters across.[9] A laid egg also contains egg white, membranes, and shell deposited around the yolk-filled ovum in the oviduct.[10] Those surrounding structures are not part of the cell.
Sources▼
- Oocyte diameter predicts the maturation rate of human immature oocytes collected ex vivo Journal of Assisted Reproduction and Genetics · 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC9596637/
- Volume and shape of normal human spermatozoa Fertility and Sterility · 1977. https://doi.org/10.1016/S0015-0282(16)42497-0
- Measurement and significance of sperm morphology Asian Journal of Andrology · 2011. https://pmc.ncbi.nlm.nih.gov/articles/PMC3739393/
- General Characteristics of Platelets NCBI Bookshelf · 2010. https://www.ncbi.nlm.nih.gov/books/NBK53455/
- Human Dorsal Root Ganglia Frontiers in Cellular Neuroscience · 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6598622/
- A Biophysical Chemist's Thoughts on Cell Size National Academies Press · 1999. https://www.ncbi.nlm.nih.gov/books/NBK224770/
- Mediterranean Species of Caulerpa Are Polyploid with Smaller Genomes in the Invasive Ones PLOS ONE · 2012. https://pmc.ncbi.nlm.nih.gov/articles/PMC3478284/
- A centimeter-long bacterium with DNA contained in metabolically active, membrane-bound organelles Science · 2022. https://doi.org/10.1126/science.abb3634
- What determines cell size? BMC Biology · 2012. https://pmc.ncbi.nlm.nih.gov/articles/PMC3522064/
- Avian Physiology: Are Birds Simply Feathered Mammals? Frontiers in Physiology · 2020. https://pmc.ncbi.nlm.nih.gov/articles/PMC7680802/
Founder and computational chemist, ProteinIQ
Dr. Matic Broz is the founder of ProteinIQ and a computational chemist. He completed a PhD focused on protein structure, molecular dynamics, and neural networks, and writes about structural biology and scientific software.