Erlang C

Erlang C is a mathematical formula widely used in contact center workforce management to determine the minimum number of agents (seats) required to handle an expected volume of inbound calls at a target service level.

Erlang C Formula

Agents Required = (Call Volume × AHT) / (Scheduled Time × (1 - ASL))

Where ASL is the acceptable service level (e.g., 80% of calls answered within 20 seconds).

Inputs Explained

• Call Volume: Forecasted number of inbound calls in the period (e.g., 1000 calls/hour).
• AHT: Average Handle Time — typical call duration including ACW (e.g., 6 minutes).
• Service Level Target: The percentage of calls to be answered within a target time (e.g., 80% within 20 seconds).

How AI Voice Agents Change the Calculation

When AI voice agents deflect 50% of inbound calls, the call volume input to Erlang C is cut in half. Organizations can staff 30-50% fewer agents while maintaining the same service level, generating dramatic cost savings.

Erlang C Limitations

Erlang C assumes a stable call arrival rate and fixed AHT. Real contact centers experience traffic spikes and variable call complexity. Modern workforce management software applies Erlang C as a starting point but refines staffing using real-time data.