Today’s Wonder of the Day was inspired by bell from , . bell Wonders, “how many cells are in your body?” Thanks for WONDERing with us, bell!

Are you fascinated by the incredible machines around you? On a typical day, you might ride in an automobile, talk on a smartphone, access the Internet on a computer, and watch a movie on a high-definition television.

While all of these machines are awesome examples of today's technology, they're not nearly as impressive as another complex machine. What are we talking about? Your human body, of course!

None of those other impressive machines would have any value if it were not for the human body's ability to use them. When you think about all the things your body does — much of it without any need for conscious input from you — it's clear that the human body is unmatched in its complexity and usefulness.

When you look closer at the human body, you realize it's made up of a wide variety of different and important parts. All of those parts share one thing in common: they're all made up of cells.

Cells are the tiny building blocks of life. Most of them are so small that they can only be seen through a microscope. How small are they? Cells vary in size based upon their type and function. Your human body, for example, has about 200 different types of cells. An average cell would have a volume of just four billionths of a cubic centimeter with a weight of just one nanogram!

Given that tiny size, the human body must have a lot of cells in it. So just how many cells make up the average human body? Ready to start counting? Go!

Tired yet? Yes, it would be impossible for you ever to count the number of cells in the human body. First, you can't see them! More importantly, there are simply too many to count. Scientists, however, have used some advanced mathematics to calculate what they believe to be an average number of cells in a typical human body.

How could they do this? Some scientists have tried to estimate the number of cells in the human body based upon the weight of the average cell and the weight of the average human body. Doing this simple arithmetic gave them an estimate of approximately 70 trillion cells!

Other scientists instead tried to estimate the number of cells in the human body based upon the volume of the average cell and the volume of the average human body. Calculations based upon volume gave an estimate of approximately 15 trillion cells. That's quite a difference between the two estimates.

To make things more difficult, scientists realized that different types of cells vary in their density and size within the body. To get the most accurate estimate possible, a team of scientists decided to study the volume and density of each type of cell in the human body.

For example, their studies found that the average human body has 50 billion fat cells and two billion heart muscle cells. That's a lot of cells, but red blood cells take the cake, totaling 20-30 trillion cells! And the grand total of all cells? Scientists concluded that the average human body contains approximately 37.2 trillion cells! Of course, your body will have more or fewer cells than that total, depending upon how your size compares to the average human being, but that's a good starting point for estimating the number of cells in your own body!

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