Erlang Calculator
Size voice trunks with Erlang B (blocking probability) or call-center agents with Erlang C (service level and waiting), from the traffic in Erlangs or from calls per hour and the average handle time. Everything in your browser.
How it changes with the number of lines
The highlighted row is the minimum that meets the target.
How it is calculated · Erlang B and C
1. Traffic
A (Erlangs) = calls/hour × AHT(s) / 3600.
It is the average number of circuits busy at the same time.
2. Erlang B (no queue):
the blocking probability is obtained iteratively
B = 1; for n=1..N: B = A·B / (n + A·B). We raise
N until B ≤ target.
3. Erlang C (with a queue,
requires N > A): from
EB = ErlangB(N,A),
C = EB / (1 − (A/N)·(1−EB)) is the probability of
waiting.
4. Service level
SL = 1 − C·e^(−(N−A)·t/AHT) and average wait
Wq = C·AHT / (N−A). We raise N until the
goal is met.
Runs locally in your browser · no sign-up · nothing leaves your browser.