How many cells are in the human body?

A widely cited 2013 study estimated 37.2 trillion cells in an adult body, and a 2016 study by Ron Sender and Ron Milo refined this to about 30 trillion for a 70-kilogram man. Red blood cells are by far the most common, making up about 84 percent of all human cells by number, though they are tiny. The same research estimated about 38 trillion bacteria in and on the body, overturning an old myth that bacteria outnumber our cells ten to one. Your body replaces around 330 billion cells every day, mostly blood and gut lining cells. The largest human cell is the egg cell, and some nerve cells can be over a metre long.