Two modifications of the mass action law are considered as applied to defining the critical micelle concentration (CMC) via constant K of the law. The first, traditional, modification defines the CMC as K1/(1−n), where n is the aggregation number, and the second one—as (Kn)1/(1−n). In both cases, the formulation of the mass action law is extremely simplified due to the exclusion of the constant, while all concentrations are expressed in the CMC units, which is slightly lower in the second case. The second modification of the law is more adequate at moderate and low aggregation numbers, which are characteristic of reverse micelles; therefore, these two modifications are conditionally attributed to the direct and reverse micelles. For both modifications, the concentrations of micelles and monomers are analyzed as depending on the total surfactant concentration in a micellar solution, while explicit analytical expressions are derived for the inverse dependences. An explicit relation has been found between the aforementioned concentrations and the micellization degree of solution . The dependence of the critical micellization degree (corresponding to CMC) on the aggregation number has been determined.