Erlang Traffic Calculator

Calculate channel requirements and blocking probability using Erlang formulas.

Formula Type

Calculate For

Traffic Load (Erlangs)

Available Channels

Target Blocking Probability (%)

Calls per Hour

Avg Call Duration (sec)

Erlangs	2% Block	1% Block	0.1% Block
5	9 ch	10 ch	12 ch
10	16 ch	17 ch	20 ch
20	28 ch	30 ch	34 ch
50	62 ch	65 ch	72 ch
100	117 ch	121 ch	132 ch

Based on Erlang B formula (blocked calls cleared)

Erlang Formulas

P(blocking) = (A^N / N!) / Sum(A^k / k!) for k=0 to N
A = traffic in Erlangs, N = number of channels

Used when blocked calls are cleared (lost). Common for trunk dimensioning where callers hang up if busy.

P(wait) = [A^N / (N! * (1-A/N))] / [Sum + A^N/(N!*(1-A/N))]
Used for call centers where calls queue if agents busy