After all, the human body contains hundreds of different cell types, each varying in size, shape, and function. Trillions of Tiny BuildersAccording to the latest research, an average adult man has around 36 trillion cells, while an average adult woman has about 28 trillion. Red blood cells dominate the numbers, making up nearly 80 to 90 percent of all human cells because they are extremely small and the body produces them in vast quantities. For years, many believed bacteria outnumbered human cells by ten to one. Scientists now estimate that the human body contains roughly 30 to 38 trillion human cells and a similar number of bacteria.