In practice, it is used to describe the total traffic volume of one hour.
For example, if a group of user made 30 calls in one hour, and each call had an average call duration of 5 minutes, then the number of Erlangs this represents is worked out as follows:
Minutes of traffic in the hour = no. of calls x duration
Minutes of traffic in the hour = 30 x 5
Minutes of traffic in the hour = 150
Hours of traffic in the hour = 150 / 60
Hours of traffic in the hou r = 2.5
Traffic figure = 2.5 Erlangs