Bangs Flow Cytometry Absolute Count Standard™ is a precisely counted population of microspheres for estimating counts of unlabeled cells via flow cytometry. The microspheres are ~7-9μm 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.: