Call Center Staffing Calculator (Erlang C)
Enter calls per hour, average handle time, agents and your service-level target time.
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Call Center Staffing Calculator (Erlang C) by TheCalcTools
How the Call Center Staffing Calculator (Erlang C) works
Traffic intensity in Erlangs = calls per hour × handle time ÷ 3,600. Erlang C gives the probability that a caller has to wait when there are N agents; it is computed from the Erlang B formula as N·B ÷ (N − A(1 − B)).
Service level = 1 − P(wait) × e^(−(N − A) × target ÷ AHT); average speed of answer = P(wait) × AHT ÷ (N − A). The model assumes callers do not hang up and calls arrive randomly.
The formula
Worked example
Using the default values shown in the calculator:
| Calls per hour | 200 |
|---|---|
| Average handle time (seconds) | 240 |
| Agents on the phones | 16 |
| Answer-time target (seconds) | 20 |
| Shrinkage (breaks, training, absence) | 30 % |
- 200 calls an hour at 4 minutes each is 13.33 Erlangs.
- With 16 agents: 69.0% answered within 20 s, average wait 34.8 s.
Result:
| Service level (answered within the target) | 69.0% |
|---|---|
| Chance a caller waits | 38.7% |
| Average speed of answer (s) | 34.8 |
| Agent occupancy | 83.3% |
| Traffic intensity (Erlangs) | 13.33 |
| Agents to schedule including shrinkage | 23 |
Frequently asked questions
What is the 80/20 target?
A common goal: 80% of calls answered within 20 seconds.
Sources and further reading
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