ErlangC calculator

The ErlangC equation is widely used in contact centres to estimate required staff when the target service level is expressed as aiming to answer a certain percentage of calls within a given number of seconds. It is suitable for use in an inbound contact centre where every advisor is able to handle every call. Typically, the equation is applied to every 15- or 30-minute interval.

ErlangC is not suitable for use in inbound centres where there is complex multiskilling. Nor is it sensible where the advisors are given inbound calls blended with other work types such as outbound calls or email work. Please contact us if you would like assistance in selecting and implementing the correct resourcing algorithm for your operation, in order to help deliver the optimum resource match.

Click here for a pdf document that contains a proof of the ErlangC equation from first principles.

The equation itself is based on a branch of Operational Research called Queueing Theory.

The calculator below provides an estimate of the number of inbound call centre advisors required to satisfy the customer service goal. It uses the ErlangC equation applied to a 30 minute period.

The calculator returns the number of inbound advisors that should be made available. It does not make an allowance for absences such as meetings, sickness or absence. Therefore, you should schedule more than this number in order to ensure that the required number are logged on at the right time.

calls offered within half hour
average call handling time (incl. wrap) in seconds
target answer time in seconds (eg 20)
% of calls answered within target time (eg 80)

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