Call Centre Erlang Staffing Calculator – including Shrinkage


Need to make a quick staffing calculation of how many agents are needed? Then our new online call centre staffing calculator may be just the thing.

It’s free to use and requires no log-ins to get it working.

Version 2.0 (released August 2016) now includes a Shrinkage Calculation as well. If you are unsure of what is included in shrinkage then we have written a comprehensive guide on how to calculate shrinkage.

If you would prefer to get the results in Excel format then our Excel Erlang C Calculator may be a better fit.

How does the online call centre staffing calculator work?

All you need to do is put in the number of calls (it also works reasonably well with emails) per half hour and the service level that you want to achieve. The calculator then works out the number of agents that are needed to meet that service level.

The calculator uses a very clever statistical calculation called the Erlang C formula. It is the basis of queueing theory and was developed by a Danish mathematician called AK Erlang in 1917. It was very much ahead of its time and is still going strong almost 100 years later. The calculations assume a Poisson distribution of calls and look at the probability of a call being answered within a service level.

Calculator Screenshot

You simply input a number of variables

  • Call Volume – the number of calls
  • Time period – the period over which the calls arrive – typically 15 minutes, 30 minutes or 60 minutes.
  • Average Handling Time – typically includes talk time as well as after call work related to the call.
  • Required Service Level
  • Target Answer Time – Typically the industry average is between 80% of calls answered in 20 Seconds or 90% of calls answered in 15 Seconds
  • Shrinkage – This is a factor to take in to account holidays, sickness meetings etc. If you are unsure of what is included in shrinkage then we have written a comprehensive guide on how to calculate shrinkage

The calculations are quite complex and involved, but we have simplified them down to make it easier. Unfortunately, the calculations are so involved that even Call Centre Helper’s super-fast servers run out at around 400 agents.

The calculator has been released as Version 2. If you encounter any problems please leave details in the comments box below.

Click here to try out the new staffing calculator.

Need to calculate the number of agents for web chat and emails?

We have also developed a Multi-Channel call centre calculator which can mix calls emails and web chat. It can also be used as a standalone calculator. It has a really nice visualisation that shows the contacts and the calls over time.

Click here for the Multi-Channel call email and web chat calculator.

Published On: 5th Aug 2015 - Last modified: 16th Dec 2016
Read more about - Essential Call Centre Tools , , , , ,


3 Comments
  1. Staffing calculator is a Great tool, is it only for inbound? or is there any version for outbound as well

    KAK 6 Aug at 7:13 pm
  2. The Erlang calculator is designed for inbound calls. It is possible to do some form of modelling on outbound but it would not be very useful.

    For outbound calls you would need to do some form of simulation.

    Jonty Pearce 25 Aug at 5:09 pm
  3. Is there a calculator that can be used to determine how many agents are required on a live chat program whereby they take 2 or 3 chats at the same time depending on the type of chat received.

    Dave 14 Nov at 6:47 am
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