Abstract: Tissue stem cells are responsible for the maintenance and regeneration of mammalian organs, tissues, and cells, including those of humans. Convenient methods for specific and accurate counting of human and animal stem cells are needed for a wide array of applications, including but not limited to cell research, medicine, stem cell medicine, gene therapy, pharmaceutical and biopharmaceutical drug development, cell and tissue biomanufacturing and bioengineering, and environmental toxicology. The invention is mathematical algorithms that can be used to compute the tissue stem cell-specific fraction of any cell preparation, including human, from the input of the cell population doubling time of a cell preparation during culture.