Work out call capacity (erlang b) instantly with clear inputs, formula shown and shareable results.
Erlang B gives the probability that a call is blocked when all channels are busy, assuming blocked calls are cleared rather than queued. It is computed by the recursion B(n) = aB(n-1) / (n + aB(n-1)) starting from B(0) = 1. The relationship is strongly non-linear, so adding a couple of channels near the target can cut blocking by an order of magnitude.
Erlang B recursion
B(0) = 1; B(n) = a x B(n-1) / (n + a x B(n-1)); carried traffic = offered x (1 - B)
One erlang is one circuit continuously occupied. Traffic in erlangs is calls per hour multiplied by average call duration in hours.
When blocked calls wait in a queue rather than being rejected — a contact centre with hold music. Erlang B suits trunk groups where a busy signal is returned.