Resumen
The paper deals with the optimal sizing of the contact center. The most important part of the contact centers are their agents, therefore the modeling of their working time is also important. In the case of parameter which describes the number of handled calls during the peak hour also the other factors should be taken into account, such as time for hygienic break and time for other activities after serving of the customer. Such modified parameter can be used in Erlang C equation for calculation of optimal number of the contact center agents.