Call Centre Erlang Staffing Calculator – v 4.1 – Now With Day Planner


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

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

What’s new in the Latest Version?

Version 4.1 Production (released December 2017) contains the following enhancements

  • Shows the number of calculations and averages values of AHT, Service Level, Shrinkage and Occupancy
  • Chart showing the distribution of AHT

Call Distribution by Hour Across the Day

Erlang Calculator can now plan calls across the day


Version 4.0 Production (released November 2017) contains the following enhancements

  • Addition of Day Planner Functionality – shows a typical profile across the day to avoid the problems of understaffing

Version 3.2 Production (released August 2017)

  • Following extensive testing and after 15,000 calculations, the Erlang C Calculator has been upgraded to production quality

Version 3.1 Beta (released April 2017) contains the following enhancements

  • Allows you to enter a Maximum Occupancy Figure. Click here to read about Maximum Occupancy

Version 3.0 (released March 2017) contains the following enhancements

  • Able to calculate up to 10,000 Agents
  • A new improved ‘Fast Erlang’ Algorithm – can quickly compute results
  • Improved accuracy over 150 Agents
  • Tabular output that highlights what can happen if you change the number of agents

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, although this can only compute up to 600 Agents.

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.

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 3.0 – If you encounter any problems please leave details in the comments box below.

Click here to try out the new Erlang Calculator for call centre staffing.

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.

Terms and Conditions

Use of the Multi-Channel Calculator is subject to our standard terms and conditions.

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

Published On: 6th Apr 2017 - Last modified: 4th Dec 2017
Read more about - Essential Call Centre Tools , , , , ,


16 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
  4. Hi Dave

    That is in the development plans, but is not a trivial task to code, so may be a while before we can bring in this feature.

    Jonty Pearce 2 Feb at 12:44 pm
  5. Maybe I did something wrong, becouse I thing 22 agents for 15 calls, and 50 chats for a day is much more!

    Nelly 1 Feb at 11:19 am
  6. You probably have got the wrong time period – it looks as though you have been running 15 calls, and 50 chats per half hour.

    I’m guessing that you kept the default as 30 minutes for Time Period length:. There are 480 minutes in an an 8 hour day.

    Running with the 15 calls, and 50 chats for a day of Time Period length 480 minutes (using the default durations of 187 and 450 seconds) I come out with 2 agents.

    Jonty Pearce 2 Feb at 12:54 pm
  7. Is it critical to apply shrinkage to each interval? Is it invalid to apply it against staff required for a day or a week?

    Lois 16 Mar at 10:12 pm
  8. It’s best if you can apply shrinkage to each particular interval. The more granular you can get the better.

    Jonty Pearce 21 Mar at 11:51 am
  9. Great tools for the call center staff, thank you for sharing such an excellent tools with us.

    Mark Williams 17 Mar at 11:16 am
  10. Is there an easy way to calculate weekly staff requirements from hourly staff numbers produced by ErlangC calculations?

    praveen 3 Apr at 11:37 pm
  11. Once you have got the hourly staff numbers and you have applied shrinkage, then all you would need to do is work out a schedule. This is typically done in excel. You work out the shift patterns that you want by hour and then you build up the number of differnt shift until you reach the staffing requirement.

    Jonty Pearce 4 Apr at 4:35 pm
  12. Hi,

    Just a quick question in relation to the new ErlangC version 3.1 vs 3.0. The occupancy figure is different for both versions. I used this calculator the other day and it told me I would have an occupancy of 56.5% however when I placed the same data in again for version 3.1 I get 80% occupancy.

    What is the difference between the 2 versions, is the 80% occupancy before Shrinkage in version 3.1?

    Toni 7 Apr at 9:09 am
  13. Hi Toni

    I think that the difference is before and after shrinkage. Occupancy is worked our before shrinkage. I think that both versions should be comparable. If you can share with me what values you used I can check them here.

    Jonty Pearce 7 Apr at 3:05 pm
  14. Hi Jonty,

    Thank you for your response.

    We used the below values for both versions.

    Inbound calls-93
    Interval: 30 mins
    AHT-421
    Shrinkage-30%
    SLA- 80/20

    The only difference is the value in version 3.1 where we requested 80% occupancy.

    Toni 14 Apr at 10:27 am
  15. Hi,

    My team has total of 10 FTEs. We receive inventory on an average of 300 per day. Out of 10 FTEs 5 of them are able to do 23-30 per day and remaining 5 are capable of doing 8-10. So how I will apply Capacity planning for my team so that I can manage my inventory and produce more nos.

    Amar 24 Apr at 9:04 am
  16. I’m interested in hearing the response to Amar’s comment on the capacity differences of operators and how that might be considered when staffing.

    Matt Schumacher 8 May at 8:07 pm
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