Erlang C Calculator

Erlang C is the standard queueing-theory formula call centers use to calculate how many agents are needed to answer a given call volume within a target service level (e.g. 80% of calls answered within 20 seconds), accounting for the fact that calls arrive randomly and wait times aren't perfectly predictable.

Traffic intensity (in Erlangs) = (call volume × average handle time) ÷ interval length. It represents the average number of agents that would be busy at any moment if workload were perfectly smooth — the actual number of agents needed is always somewhat higher than this, to absorb random variation in call arrivals.

Because calls don't arrive in a perfectly even stream — there's natural random clustering. Staffing to exactly match average traffic intensity would mean roughly half of all calls wait in queue; extra agents beyond that average are needed to keep wait times short enough to hit your service level target.

80% of calls answered within 20 seconds ('80/20') is the most common industry-standard target, though many centers use their own target depending on the type of calls (sales vs. support vs. emergency lines).

Shrinkage is the percentage of paid time agents aren't available to take calls — breaks, meetings, training, absenteeism, etc. The Erlang C formula only tells you agents needed while actually staffed on the phones; you then divide by (1 − shrinkage%) to get the total headcount you need to schedule, since some of them will always be shrunk away at any given moment.