An apparatus and a method for ascertaining and billing for a volume of air generated by an air-conveying device. The air quantity ascertaining and billing apparatus has an air-conveying device generating an air volume flow through an air passage. A measuring device measures air-related parameters of the particular air volume flow. An analysis unit analyzes the measured parameters, in order to determine the total air volume that was conveyed by the air conveying device through the air passage over a period. A transfer device transfers the value determined for the air volume by the analysis unit to a validation device. The validation device links the air volume flow or the determined air volume to an economic value, in order to obtain a billing value for the generated air volume.