Erlang is a unit that is used in telephony to measure “load” (or the volume of calls or chats) on a system (such as a call center ACD). Erlang is also a programming language developed by the telephone services provider Ericsson.
For the purposes of our definition of Erlang, we will be referring to the Erlang formulas that have been developed to perform staffing and capacity forecasting. The most common Erlang formula for this purpose is known as Erlang C (which is the simplest Erlang formula).
The Erlang C formula uses several variables to predict the service level that will be provided based on those variables. For example, Erlang C can be used to predict the percentage of calls that are answered (rather than queued) given a forecasted call volume, the number of agents, and the average handle time of those calls.
The forecasted call volume is typically forecast for a given time period (such as an interval of 15 or 30 minutes).
Erlang C has been used in call centers to show that there are benefits to using a single call center platform (which makes sense — if agents are distributed across multiple platforms, it is impossible to route calls across all the agents in a way to improve the answer rate). Further, it has been shown that blended agents and campaigns are more efficient. That is, when agents are trained to handle different calls from different campaigns, and the ACD is configured to blend campaigns, efficiencies are obtained.
Another version of Erlang that is more accurate (and that includes a variable related to call abandons) is Erlang X. Erlang X includes more features in the model and is therefore more accurate.
Erlang calculations may be used for call center staff scheduling as well as capacity planning. A number of excellent Erlang calculators are available, including those by ccmath.com.