The first one estimates the number of cells in a 100-kilogram male using an average cell volume of between 1,000 and 10,000 cubic micrometers. This gave them a “back of the envelope estimate” in a range of 30 to 40 trillion cells.

Next, they calculated the actual cell number of the five most common cell types in an average adult male, which account for 97 percent of the cells in the body. This led them to an estimate of 30 trillion cells, of which red blood cells make up 84 percent.

But human cells are not the only cells in our bodies. Although previous studies have estimated that there are 10 times as many bacteria in our bodies than human cells, Prof. Milo and colleagues revised this number to be around 38 trillion.

Interestingly, although large in number, bacteria are much smaller than human cells, and they actually make up only 200 grams of total body mass, according to Prof. Milo.

But with nearly equal numbers of cells in our bodies, one could argue that we are as much bacteria as we are human, bringing the total number up to around 70 trillion.