FREE · NETWORK & IT INFRASTRUCTURE
Erlang B & C Calculator.
Find the phone lines or trunks needed for a blocking target (Erlang B) or the call-centre agents needed for a service level (Erlang C).
- Offered traffic
- 15 erlangs
- Blocking with these lines
- 0.839 %
- G.711 bandwidth for all lines
- 2.09 Mbps each way
Blocking around the answer
| Lines | Blocking | Calls lost per busy hour |
|---|---|---|
| 20 | 4.559 % | 13.7 |
| 21 | 3.154 % | 9.5 |
| 22 | 2.105 % | 6.3 |
| 23 | 1.354 % | 4.1 |
| 24 | 0.839 % | 2.5 |
| 25 | 0.501 % | 1.5 |
| 26 | 0.288 % | 0.9 |
| 27 | 0.16 % | 0.5 |
| 28 | 0.086 % | 0.3 |
- Erlang B assumes blocked calls are lost (not queued) and random arrivals. Use the busiest hour of a typical busy day.
How to use Erlang B & C Calculator
Choose lines (Erlang B) or agents (Erlang C), enter busy-hour calls and average duration, then the blocking or service-level target.
How it works
Traffic in erlangs = calls × duration ÷ 3,600. Erlang B uses the standard recursion; Erlang C derives the waiting probability from it and the service level from the exponential waiting time.
Example
300 calls of 3 minutes in the busy hour = 15 erlangs, needing 24 lines for 1 % blocking.
Questions about Erlang B & C Calculator
Is Erlang B & C Calculator free, and do I need an account?
Yes. This tool is free to use in your browser without an account. Processing takes place on your device.
What are the limits and what should I check?
Erlang B assumes blocked calls are lost; Erlang C assumes callers wait without abandoning. Traffic up to 5,000 erlangs. Everything is calculated in your browser; nothing is sent or probed on the network. Review the result before using it in your work.
Is my input sent to a server?
Your input is processed in your browser and is not uploaded by this tool. Files and pasted text are cleared when the page is refreshed. Normal website requests are still required to load the page and its libraries. Read the privacy explanation.