Our Flow Cytometry Absolute Count Standard is a precisely counted population of microspheres for estimating counts of unlabeled cells via flow cytometry. The microspheres are 7-9um in diameter and supplied at 1e+6 beads/mL. Beads are internally labeled with multiple fluorophores for excitation with common lasers (e.g. 488nm, 633nm) and discrimination from the cell population. By evaluating the ratio of microspheres to cells, the volumetric number of cells may be determined.