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Erlang B and C Queueing Theory Calculator

Call blocking (B) and waiting probability (C) formulas.

Calculates the Erlang B formula for call blocking probability and Erlang C for probability of queuing in a M/M/c telephone traffic model. Traffic in Erlangs A = λ/μ.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

B = A^N/N! / Σ(A^k/k!); C = B·N/(N−A·(1−B))

In depth

Calculates the Erlang B formula for call blocking probability and Erlang C for probability of queuing in a M/M/c telephone traffic model. Traffic in Erlangs A = λ/μ.