Great question! Amazingly, an adult human body contains about 50-100 trillion cells (that´s 100,000,000,000,000)! A lot of zeros, right!? So how do we get this number? Well it actually is not that complicated, mathematically.

First, we assume that an average eukaryotic (animal) cell is about 10 micro meters across (it has a diameter of 10 micro meters, also called microns). Then we assume that a human cell is a cube (as opposed to being a sphere or some other shape). This allows us to calculate the volume of the cell as 10x10x10 cubic microns = 1000 cubic microns. Since there are one billion cubic microns in a cubic millimeter (mm, the smallest lines on a centimeter ruler), we can make the next calculation that there are one million cells in a cubic mm. Ok, so now we can take it up another measurement as we know that there are one million million cells in a cubic decimeter, and one cubic decimeter is the same as one liter. In other words, there are one trillion cells in one liter of volume.

Next, we assume that 1 liter is about the same as 1 kilogram (kg) because this is the conversion that works for water (and we are mostly water after all). Now we know that there are roughly 1 trillion cells in one kilogram. How many kg are you? I´m about 53 kg, meaning I have about 53 trillion cells in me! How many trillion cells do you have in you?

No one really knows the exact number of cells, but we can approximate to about 10-50 trillion. Cells are always created and destroyed in the human body. About 300 million cells die every minute in our bodies! Since different cells have different jobs in our body, there are about 210 different "types" of cells. Something interesting is that about 95% percent of cells found in our body are bacterial cells mainly in your digestive tract.

Cells are so small that they are really hard to see unless under a microscope. When you rub the inside of your cheek, you get thousands of cheek cells onto your finger, and when you brush off your hand millions of skin cells come off.