Erlang ‘C’ & Scheduling for Call Centres

Erlang ‘C’ is a Nobel winning formula used in the Call Centre and Operations industries to determine the correct and appropriate level of staffing based on key call metrics.  The scary looking formula for this is below and the even scarier explanation from Wikipedia is here.

From a Call Centre and Staffing Point of view, the primary elements considered are as follows:

• Average Talk Time
• Calls/per specified period (15min is a good benchmark)
• Specified Service Metrics or SLA (ie. 80/20 <- 80% of calls answered in 20s or less etc…) … correspondingly, you want to consider your abandon %’age here also.  Are you willing to accept that some of your customers will hang up?  If so, how many & consider what impact that will have on your business in the long run!

With this information in hand and using the formula, you are able to determine how many resources you need in a given period to meet your customer demand.  Using some free online tools (links provided below), you are also able to determine your required resources based on a specified timetable and rotation.  For example, if the formula states you need 8 resources between 8am-9am and you are running a 24/7 call center the actual number of staff you need to employ is ‘X’.

Some Good Free Erlang ‘C’ Calculators –

• Online Traffic Calculators
• Erlang ‘C’ Calculator
• This last one is a downloadable application & HIGHLY RECOMMENDED

Holiday/Vacation/Sickness –

With this in mind, you still need to plan for excess capacity relevant to staff absenteeism either planned or unplanned.  So although the formula only called for 8 staff & your overage based on a 24/7 call centre is ‘X’ … you should actually plan to have ‘Y’ resources available to cover these gaps!!