Question 1

What is the Erlang C formula?

Accepted Answer

Erlang C is a mathematical queuing model that calculates the number of agents needed to handle a given call volume at a specified service level. It accounts for callers who wait in queue (unlike Erlang B, which assumes busy signals). It requires three inputs: call arrival rate, average handle time, and target service level.

Question 2

What is a good occupancy rate for a contact centre?

Accepted Answer

The optimal occupancy rate is 78–84%. Above 85% causes agent burnout, quality degradation, and increased attrition. Below 70% indicates overstaffing. The sweet spot balances agent wellbeing with cost efficiency.

Question 3

How many agents do I need for my call centre?

Accepted Answer

Use the Erlang C calculator above: enter your calls per hour, average handle time in seconds, target service level percentage, and target answer time. The calculator outputs the minimum agents required and the resulting occupancy rate.

Question 4

What is the difference between Erlang B and Erlang C?

Accepted Answer

Erlang B calculates trunk (phone line) capacity assuming no queuing — callers receive a busy signal. Erlang C calculates agent staffing assuming callers wait in queue. For contact centre staffing, always use Erlang C.

Question 5

How does AHT affect agent staffing?

Accepted Answer

AHT directly impacts required headcount. A 10-second AHT increase on a 1,000-agent operation typically requires 15–20 additional FTE. Always forecast AHT separately from volume — AHT variance is a common source of staffing miscalculation.

Erlang C Calculator

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