Ratio of virion particles present as determined microscopically to number of plaques that the same stock is capable of producing.
Contrast absolute efficiency of plating with relative efficiency of plating, with the latter generally used synonymous with simply efficiency of plating (EOP). See also efficiency of center of infection (ECOI).
Absolute efficiency of plating is not often determined and otherwise is limited by the potential to distinguish whole phage particles from incomplete phage particles. Nevertheless, the concept is real one. Alternatively, note that it is possible to compare titers are determined via plaque count with titers are they are determined using killing titer assays.
At least in principle, the following relationship should hold (brackets are indicative of concentrations):
[Total virion count] ≥ [Killing titer] ≥ [Plaque-forming units]
That is, there may be more microscopically countable virion particles, i.e., as via electron microscopy, than there are virions that are present which are capable of killing bacteria than there are virions that are capable of forming plaques, with
[Plaque-forming units]/[Total viron count] = Absolute efficiency of plating.
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