In 1946, the International Consultative Committee on Telephones and Telegraphs, honoured A K Erlang, by adopting the name 'erlang' for the basic unit of telephone traffic.

An Erlang is a 'dimensionless unit', a unit of measurement of traffic density in telecommunications systems.  The Erlang describes the total traffic volume of one hour - one Erlang is usually defined as 60 minutes of traffic.

If a supermarket had 5 checkouts, and during the busiest hour of the day they are all busy the whole time, this would represent 5 Erlangs of traffic.

Let us look at a one-hour calculation for 120 calls with a 2.5 minute duration:

Minutes of traffic in the hour

= 120 x 2.5 = 300

Hours of traffic in the hour

= 300 / 60 = 5

Traffic figure = 5 Erlangs