Calculate viral titer in plaque-forming units per milliliter (PFU/mL) from plaque assay counts, and determine the multiplicity of infection (MOI) for infection experiments. Use this tool when quantifying phage or virus stocks — a well-designed plaque assay produces 30–300 plaques per plate at a countable dilution, and the titer is essential for planning reproducible infections. A low MOI (below 1) ensures most cells receive at most one virion, while a high MOI (above 10) guarantees infection of nearly every cell in the culture.
About PFU and MOI
Plaque-forming units (PFU) per milliliter measures the concentration of infectious virions in a sample, determined by counting plaques formed on a lawn of susceptible cells. Multiplicity of infection (MOI) is the ratio of infectious virions to target cells, a critical parameter for infection experiments. A well-designed plaque assay uses countable plates (30–300 plaques) at appropriate dilutions.
