Erlang Calculator
Calculate call blocking probability (Erlang B) and waiting probability (Erlang C) for telecom and call center planning.
Erlang Calculator
How to Use the Erlang Calculator
- Select Erlang B (blocking) or Erlang C (queuing) mode.
- Enter the traffic intensity in Erlangs and the number of channels or agents.
- For Erlang C, optionally enter average handle time and target answer time.
- Click Calculate to get blocking probability, wait probability, and service level.
Quick Reference
| From | To |
|---|---|
| 1 Erlang, 5 channels | ~0.83% blocking (B) |
| 5 Erlangs, 10 channels | ~18.1% blocking (B) |
| 10 Erlangs, 15 agents | ~57% wait probability (C) |
| 10 Erlangs, 20 agents | ~17% wait probability (C) |
Use Cases
- •Dimensioning telephone trunk groups to meet a target grade of service.
- •Staffing call centers to achieve a desired service level agreement.
- •Planning VoIP gateway capacity for enterprise phone systems.
- •Analyzing queuing behavior in customer service and support operations.
Formula
Erlang B: B(N, A) = (A^N / N!) / Σ(k=0 to N)(A^k / k!). Erlang C: probability of a call waiting = C(N, A) based on traffic intensity A and N agents.
Frequently Asked Questions
What is Erlang B?
Erlang B calculates the probability that an incoming call will be blocked (lost) when all channels are busy. It is used for dimensioning trunk groups in telephone networks where blocked calls are simply rejected.
What is Erlang C?
Erlang C calculates the probability that a call will have to wait in a queue before being served. It assumes blocked calls wait rather than being dropped, making it the standard model for call center staffing.
What is traffic intensity in Erlangs?
Traffic intensity (A) is measured in Erlangs and equals the average call arrival rate multiplied by the average call duration. For example, 10 calls per hour each lasting 3 minutes gives A = 10 × (3/60) = 0.5 Erlangs.