--- title: "How many cells are in the human body? about 30 trillion human " description: "about 30 trillion human cells, plus 38 trillion bacteria How the figure is estimated, how confident it is, and what makes the scale graspable." url: https://atoneplace.net/how-many/cells-in-the-human-body/ site: "At One Place" --- # How many cells are in the human body? **How many cells are in the human body?: about 30 trillion human cells, plus 38 trillion bacteria** Red blood cells are 84% of your cells by number but about 4% of your mass. Muscle and fat cells are 75% of the mass and 0.2% of the count. A careful 2016 recount put the reference adult male at about 30 trillion human cells and roughly 38 trillion bacteria — a ratio of about 1.3 to 1, not the 10 to 1 that textbooks repeated for forty years. The old ratio traced to a single 1972 back-of-envelope estimate that was never checked. The composition is also surprising: about 84% of human cells by number are red blood cells, which are tiny and have no nucleus, while the cells that make up most of the body's mass — muscle and fat — are a rounding error by count. ## How the figure is arrived at Organ by organ, rather than dividing body mass by an average cell size. For each tissue, take its mass and divide by the measured mass of a typical cell of that type, using histology data. That approach is what exposed the error: red blood cells dominate any count, and any method that ignores cell-type differences gets the answer badly wrong. ## How confident it is - **Low estimate:** 25,000,000,000,000 - **High estimate:** 35,000,000,000,000 - **Spread:** 1.4× between the bounds ## Other the human body counts - [How many bones are in the human body?](https://atoneplace.net/how-many/bones-in-the-human-body/) — 206 in an adult — about 300 at birth - [How many neurons are in the human brain?](https://atoneplace.net/how-many/neurons-in-the-brain/) — about 86 billion - [How many muscles are in the human body?](https://atoneplace.net/how-many/muscles-in-the-human-body/) — about 600 skeletal muscles - [How many hairs are on your head?](https://atoneplace.net/how-many/hairs-on-your-head/) — about 100,000 - [How many taste buds do you have?](https://atoneplace.net/how-many/taste-buds/) — about 2,000 to 8,000 - [How long are all your blood vessels?](https://atoneplace.net/how-many/blood-vessels-length/) — commonly quoted as 100,000 km — but probably closer to 20,000 - [How many base pairs are in human DNA?](https://atoneplace.net/how-many/dna-base-pairs/) — about 3.1 billion per copy — 6.2 billion in most cells ## Common questions ### How many cells are in the human body? about 30 trillion human cells, plus 38 trillion bacteria ### How is that estimated? Organ by organ, rather than dividing body mass by an average cell size. For each tissue, take its mass and divide by the measured mass of a typical cell of that type, using histology data. That approach is what exposed the error: red blood cells dominate any count, and any method that ignores cell-type differences gets the answer badly wrong. ## Related pages - [How many bones are in the human body?](https://atoneplace.net/how-many/bones-in-the-human-body/) - [How many neurons are in the human brain?](https://atoneplace.net/how-many/neurons-in-the-brain/) - [How many muscles are in the human body?](https://atoneplace.net/how-many/muscles-in-the-human-body/) - [How many hairs are on your head?](https://atoneplace.net/how-many/hairs-on-your-head/) - [How many taste buds do you have?](https://atoneplace.net/how-many/taste-buds/) - [How long are all your blood vessels?](https://atoneplace.net/how-many/blood-vessels-length/) - [How many base pairs are in human DNA?](https://atoneplace.net/how-many/dna-base-pairs/) - [How many people are there in the world?](https://atoneplace.net/how-many/people-alive-right-now/) - [How many stars are there in the universe?](https://atoneplace.net/how-many/stars-in-the-universe/) - [How many countries are there in the world?](https://atoneplace.net/how-many/countries/) - [How many grains of sand are there on Earth?](https://atoneplace.net/how-many/grains-of-sand-on-earth/) - [How many ants are there in the world?](https://atoneplace.net/how-many/ants-on-earth/) - [How many trees are there in the world?](https://atoneplace.net/how-many/trees-on-earth/) ## Sources - Typical range compiled from manufacturer specifications — At One Place (/about/)