measuring the total amount of DNA 10^13  counting number of cells in 1 g of tissue 3.5X10^13 cells/body
||Human Homo sapiens
||Renato Baserga, "The Biology of Cell Reproduction" 1985 Harvard University Press, p.52 bottom paragraph and p.53 top paragraph
||"It is possible to calculate, approximately, the number of cells in an animal by  measuring the total amount of DNA. For instance, a mouse 25 grams in weight contains a total of 20 mg of DNA. Since diploid somatic cells (in mammals) have 6X10^-12 g of DNA, one can calculate that there are, in mouse, ~3X10^9 cells. By extrapolation, a 70 kg man should have in the order of 10^13 cells. A slightly different estimate  —3.5X10^13 cells—is obtained if one counts the number of cells in 1 g of tissues, which has roughly 5X10^8 cells. Incidentally, as one can see from table 4.1, the mass of a diploid liver cell in the rat is 2X10^-9 g, which again would give 5X10^8 cells. These figures are very approximate and should serve only as a guide."
||"It does not take a profound observer to realize that the most important mechanism in the growth of tissues is an increase in cell number, since all animals derive from a single fertilized egg cell. The adult rat liver alone has almost 2X10^9 cells, though the liver is much more cellular than the animal as a whole, which contains bones, tendons, cartilage, and other tissues that have a lot of intercellular substance and few nuclei."