Erlang B Blocking Calculator
Calculate call blocking and carried traffic for a finite pool with no waiting room.
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Calculation steps
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How to calculate
Convert offered arrival workload to erlangs and use stable Erlang-B recursion.
A=arrivals/hour×mean holding hours; B₀=1; Bc=A Bc−1/(c+A Bc−1)
Worked example
Offered load 1 erlang and two channels give blocking probability 20% and carried traffic 0.8 erlang. With no offered traffic and at least one channel, blocking is zero.
Assumptions and input details
Use 1–2000 channels, nonnegative arrival rate and positive holding time; offered load must be at most 1e6 erlangs. Arrivals follow a stationary Poisson model, channels are identical, and blocked calls leave without queuing or retries. This is a loss system, distinct from Erlang-C waiting-time staffing. The target is entered by you; the minimum-channel search stops at 2000 and reports when a target is not reached.
References: Cisco: traffic analysis and Erlang-B assumptions
Unit definitions
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Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
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Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
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