Elements of Staffing the Inbound Call Center

Determining Proper Call Center Staffing Requirements is Key to Success

By Ellis Smith

Operation and management of inbound call centers is a specialized field serving healthcare, as well as retail, wholesale, service, and hundreds of other applications. A major telecommunications tool to help run these centers effectively is ACD (automatic call distribution). In recent years, ACD software has become extremely sophisticated and can include outbound calling, Web chat, skills-based routing, and Interactive Voice Response (IVR) right out of the box. It also provides information to project appropriate staffing requirements needed for optimal operation.

Small call centers of two to four people often “run themselves” because call traffic is low, and the people can visually manage callers in queue or can be sure someone is available to answer calls. In these small centers, an ACD may not be needed.

As volume and call center size increase, it can become a daunting task for those unfamiliar with call center management techniques to manage the people and call volume efficiently. Many organizations have rolled out ACD extensively and for the most part, thoughtfully.  With ACDs, most organizations see immediate improvements in productivity and service quality.

ACD vendors teach how the reports are created and help with the set up of call routes and groups. However, the one thing that the vendor never teaches is how to optimize staff and technology to provide the best benefit to the organization and its customers. The truth is that you cannot maximize the investment in ACD technology unless the call center manager understands the basic theories and principles of running call centers and not just the reporting capability.

The elements for determining the appropriate staffing requirements are relatively simple:

Call Volume

Forecast this data using historical data, known variations, and human intuition. (Data source: ACD or call center software)

Typical Percentages of Calls

An arrival rate (AR) study of one typical week’s hour-by-hour traffic will give a starting point (see “Arrival Rate” chart). Surprisingly, statistics do not vary much in percentage. That is, if 15% of your daily calls were between 9:00 a.m. and 10:00 a.m. and 25% of the weekly calls arrive on Monday, this particular percentage will hold true enough for all your initial arrival rate planning.

Sample Arrival Rate
  Monday Tuesday Wednesday Thursday Friday Week Total
1 Hour Ending Total % Total % Total % Total % Total % Total %
  9.0 100 5% 55 3% 59 4% 42 3% 62 5% 318 4.1%
10.0 240 12% 194 11% 178 12% 168 12% 162 13% 942 12.1%
11.0 270 14% 261 15% 225 15% 213 15% 200 16% 1169 15.0%
12.0 230 12% 223 13% 193 13% 183 13% 175 14% 1004 12.9%
13.0 180 9% 172 10% 133 9% 112 8% 112 9% 709 9.1%
14.0 220 11% 189 11% 148 10% 154 11% 125 10% 836 10.7%
15.0 250 13% 223 13% 178 12% 183 13% 150 12% 984 12.6%
16.0 230 12% 206 12% 178 12% 168 12% 137 11% 919 11.8%
17.0 140 7% 120 7% 119 8% 112 8% 87 7% 578 7.4%
18.0 90 5% 70 4% 74 5% 70 5% 37 3% 341 4.4%
Totals 1950 25% 1713 22% 1485 19% 1405 18% 1247 16% 7800 100%

Average Talk Time

This is the time spent actually on each call. The national average for inbound triage calls is less than ten minutes; for referral and registration calls, it is between four and five minutes. Your average talk time can be established more precisely by using the ACD stats already available. (Data source: ACD)

After Call Work Time 

This can be a big factor in call planning. If agents spend half their time on tasks unrelated to inbound calls, you can only count them as half an agent in planning for call volume. This category offers the greatest opportunity for abuse and for potential improvement in service. Many call centers do have legitimate after-call-work-time. This can be measured and averaged easily so that individual staff results are closely monitored. (Data source: ACD or call center software)

Service Level

The service level is the percentage of inbound calls expected to be answered in a given number of seconds. Ninety-five percent within thirty seconds or ninety percent within twenty seconds are two widely used service levels. Each organization establishes their own expectations for service based on their own needs and capabilities. Some criteria used to establish service levels are:

  • The value of the call to the caller and the receiver
  • Competitive nature of the organization
  • Budget and labor cost
  • Facility costs (trunk lines, equipment, usage charges, and so forth)
  • Caller tolerance (how long will they hold before hanging up; whether they have an alternative service to call)
  • The organization’s desire to provide good service

Number of Staff Required

From the above criteria, hour-by-hour staffing requirements can be established using industry standard blocking theories, such as Erlang. These are the same standards used by virtually all modem call centers (see “Call Center Requirement” chart):

Sample Call Center Requirement
Time% ofCallsAgents
7 to 80%0 
8 to 94%808
9 to 1012%23617
10 to 1115%29321
11 to 1213%25218
12 to 19%17714
1 to 211%20916
2 to 313%24618
3 to 412%23017
4 to 57%14412
5 to 64%868


These are established based upon the staffing requirements. Gantt charting is a popular method of creating schedules and making the numbers visual.

Once these steps are taken, scheduling and planning become easier. A completed study includes all expected ranges of calls and need not be repeated until the manager feels that circumstances have rendered the original study no longer representative. It is also useful to calculate staffing requirements for anticipated volume fluctuations, such as seasonal differences in triage, response to advertising, etc. If staff or infrastructure is needed to maintain the desired service level, it can be easily justified.

Having the right person managing call center staff is essential.  The above process is more or less the “math” of management. However, it doesn’t address the “people” side: interviewing, hiring, training, coaching, and creating a culture of service so good performers will stay with the call center.

The supervisor’s job is a tough one. Most have been good performers as agents and move into supervision as the natural course of career advancement. They have many duties, but the most critical is having the right number of people on the phone at the right time, often a minute-by-minute job maximizing the performance of the call center operation.

Ellis Smith is the president of Telecom Management Group.

[From the October/November 2008 issue of AnswerStat magazine]