Humans are complex organisms made up of trillions of cells, each with their own structure and function.

Scientists have come a long way in estimating the number of cells in the average human body. Most recent estimates put the number of cells at around 30 trillion. Written out, that’s 30,000,000,000,000!

These cells all work in harmony to carry out all the basic functions necessary for humans to survive. But it’s not just human cells inside your body. Scientists estimate that the number of bacterial cells in the human body likely exceeds the number of human cells.

There are about 200 different types of cells in the body. Here are just a few examples:

  • red blood cells (erythrocytes)
  • skin cells
  • neurons (nerve cells)
  • fat cells

Humans are multicellular, complex organisms. The cells inside our bodies are “specialized.” This means that each type of cell performs a unique and special function. For this reason, each of the 200 different types of cells in the body has a different structure, size, shape, and function, and contains different organelles.

For example:

  • Cells in the brain may be longer in shape so they can transmit signals more efficiently.
  • Cells of the heart have more mitochondria because they need a lot of energy.
  • Cells in the respiratory system are responsible for taking up oxygen and releasing carbon dioxide.

All the cells work together to keep the human body running efficiently.

An average person is estimated to contain roughly 30 trillion human cells, according to recent research.

This is, of course, a rough approximation. It’s extraordinarily complicated to count human cells. It’s not as simple as figuring out the size or weight of a single cell and making an estimate based on the volume of the human body.

Each of the 200 different types of cells in the human body has a different weight and size. Within the body, some cells are packed more densely, while others are more spread out.

Cells are constantly dying, and new ones are being made simultaneously. On top of that, the actual number of cells will vary from person to person, depending on their age, height, weight, health, and environmental factors.

The best we can do is find an estimate based on an average person. A recent study used a man between 20 and 30 years of age, weighing 70 kilograms (154 pounds) and measuring 170 centimeters (5 feet, 7 inches) in height, as a reference.

In the study, researchers went through each cell type and used a variety of tedious methods to estimate the number of each type. They used the most up-to-date information available to make a detailed list of volumes and densities in every organ of the body. Once they arrived at an estimate of all the different cell types, they added them all together. The number they arrived at was 30 trillion.

You may have read that bacterial cells in the human body outnumber human cells 10 to 1. The primary source for that ratio dates back to the 1970s, when American microbiologists used a series of assumptions to calculate the number of bacteria inside the intestinal tract.

The 10:1 ratio has since been disproven.

New data show that the number of bacterial cells inside a human body is around 38 trillion. This turns out to be much closer to the estimated 30 trillion human cells in the body.

So, while there are likely more bacterial cells than human cells in your body at any given time, the difference isn’t as great as previously thought.

There are three types of blood cells: red blood cells, white blood cells, and platelets. Red blood cells (RBCs) are by far the most abundant type of cell in the human body, accounting for over 80 percent of all cells.

Adult humans have somewhere around 25 trillion RBCs in their body, on average. Women usually have fewer RBCs than men, while people living at higher altitudes will usually have more.

There are also about 147 million platelets and another 45 million lymphocytes (a type of white blood cell) in the body, based on recent calculations.

There are roughly 171 billion cells in the average male brain according to new research, including about 86 billion neurons. Neurons are cells that help transmit signals throughout the brain. There are also 85 billion other cells in the brain, called glial cells, that help support the neurons.

It’s difficult to measure exactly how many cells your body makes on any given day. The lifespan of each of the 200 types of cells varies considerably, so not every type of cell is produced at an equal rate.

A good start is to look at the number of RBCs that are produced each day, as RBCs are the most abundant type of cell in the body. RBCs live for about 120 days, at which point they are removed from circulation by macrophages in the spleen and liver. At the same time, specialized stem cells are replacing the dead red blood cells at roughly the same rate.

The average body makes about 2 to 3 million red blood cells every second, or about 173 to 259 billion red blood cells per day.

Most, but not all, cells in the body will eventually die and need to be replaced. Fortunately, a healthy human body is capable of maintaining a precise balance between the number of cells produced and the number of cells that die.

For example, as the body is producing between 173 and 259 billion RBCs per day, roughly the same number of RBCs are dying off.

It’s challenging to figure out exactly how many cells in the human body die each day. Cells aren’t created equal when it comes to the length of their life cycles. For example, white blood cells only live for about 13 days, whereas red blood cells live for about 120 days. Liver cells, on the other hand, can live up to 18 months. Cells in the brain will stay alive throughout a person’s life.

Using more sophisticated methods than before, new research estimates that there are about 30 trillion human cells in the average person. Red blood cells comprise the majority of these cells.

Of course, human cells are not the only cells in our bodies. New research has also learned that there are around 38 trillion bacteria in the average human as well. This brings the grand total to over 68 trillion cells (human or not).

This is by no means the final estimate for the number of cells in the human body, but it’s a good start. Over time, scientists will continue to fine-tune these calculations.