Question 1

What is the Erlang C formula used for in call centers?

Accepted Answer

The Erlang C formula calculates the probability that a call must wait in queue and determines the minimum number of agents needed to meet a service level target (e.g. 80% of calls answered within 20 seconds). It uses traffic intensity in Erlangs, number of agents, average handle time, and target answer time.

Question 2

How do you calculate Erlang C for a chat center with concurrency?

Accepted Answer

For chat centers, divide traffic intensity by the concurrency factor: A = Chats × AHT / (Interval × Concurrency). If agents handle 3 chats simultaneously, effective traffic drops by 3×. Service level and wait time calculations should also use effective AHT = AHT / concurrency.

Question 3

What is the difference between Erlang C and Erlang A?

Accepted Answer

Erlang C assumes no caller abandonment — all contacts wait indefinitely, making it conservative. Erlang A (M/M/N+M model) accounts for callers who leave the queue, using an average patience parameter. Erlang A typically recommends 5-15% fewer agents for the same service level.

Question 4

What is shrinkage in call center workforce management?

Accepted Answer

Shrinkage is the percentage of paid time agents are unavailable to handle contacts — including breaks, training, meetings, absences, and system downtime. Typical range is 25-35%. Formula: Scheduled Agents = Raw Erlang Agents / (1 - Shrinkage%). A 27% shrinkage means you need 1.37× the Erlang-calculated agents.

Question 5

What is a good occupancy rate for a call center?

Accepted Answer

The recommended occupancy range is 80-87%. Below 70% indicates overstaffing. Above 90% leads to agent burnout, quality degradation, and high attrition. Occupancy = Traffic Intensity (Erlangs) / Number of Agents.

Question 6

How do you calculate traffic intensity in Erlangs?

Accepted Answer

Traffic Intensity (Erlangs) = Call Volume × Average Handle Time / Interval Duration. For example: 200 calls in 30 minutes with 180s AHT = 200 × 180 / 1800 = 20 Erlangs. For chat centers, divide by concurrency.

Question 7

What is the 80/20 rule in call centers?

Accepted Answer

The 80/20 rule is a common service level target: 80% of calls answered within 20 seconds. This is used as an input to the Erlang C formula to calculate the minimum number of agents needed to achieve this target.