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Erlang C calculator

The reference mathematical formula for sizing a call center. Enter call volume, average handling time and service target to get the number of agents required.

Your data

All data for a one-hour period:

Incoming call volume over one hour
Average handling time (conversation + after-call work)
% of calls answered within the target delay
Example: 80% of calls answered within 20s
Non-productive time (breaks, meetings, training)

Enter your numbers and click Calculate.

What is Erlang C?

Erlang C is the world standard for call center sizing. The formula takes into account call volume, handling time, service target and target delay to calculate the number of agents needed.

The original formula does not include shrinkage. We add it afterwards to get the number of agents to hire. A one-third shrinkage means you need 1.43 paid agents to have 1 productive agent.

This tool uses an approximation of Erlang C that is good enough for operational sizing. For precise WFM planning, use a dedicated tool such as NICE, Verint or Calabrio.

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