Erlang Calculator - for Call Centre Staffing (Online Version 5.0)

Now with Week and Month Planner and Upload Facility

Call Centre Erlang Calculator
Calculate the number of staff required to reach an agreed service level
Incoming contacts
Hours open per day
Distribution of calls by day

% Total
Average Handling Time (AHT)
Required Service Level
% Answered in
Target Answer Time
Show Advanced Options

Statistics from All Erlang Calculations

Number of Erlang Calculations performed
Past 24 Hours Past Month
3,489 69,742

Average Values Entered
AHT (Seconds) 370
AHT (Minutes) 06:10
Average Service Level 81.5%
Average Target Answer Time (Seconds) 35.1
Average Shrinkage 27%
Average Max Occupancy 83.7%
Above figures include calls and other work tasks

How To Use This Erlang Calculator

  1. If you have 200 calls per hour, then enter the number of incoming contacts as 200 and the period is 60 minutes.
  2. The Average Handling Time is the amount of time that a person (an agent) takes to handle a phone contact. This includes the talk time as well any paperwork time (wrap-up time) before they are able to answer the next call. This should be in seconds.
  3. Put in your Service Level target and time. So if you wanted to handle 90% of calls in 15 seconds, put in 90 and 15. If you are uncertain of this the industry "average" is 80% of calls answered in 20 seconds.
  4. This contact centre staffing Erlang calculator is a hybrid model based on both the Erlang C formula the Erlang A formula. The Erlang C formula was invented by the Danish Mathematician A.K. Erlang and is used to calculate the number of advisors and the service level. Call Abandons are calculated using the Erlang A formula which was devised by Swedish statistician Conny Palm in 1946. This assumes an Average Patience - also know as Average Time to Abandon (ATA).
  5. We also have a more flexible Microsoft Excel based version of this calculator. You can download the free Excel Erlang Calculator
  6. This calculator works on probabilities, so may appear to overstate the number of agents needed at low levels. So for example if you enter 0 calls per hour it will say that you need 1 agent. This is quite correct, as there may be a possibility that one call may come in. In practicality, you may decide to not schedule any staff.
  7. The maximum number of agents that the calculator can calculate before shrinkage is applied is 10,000 Agents.
  8. Shrinkage is a factor designed to take into account holidays, sickness etc. For more information Read this article on how to calculate shrinkage
  9. The maximum occupancy is designed to improve accuracy. If you take Occupancy over 85% - 90% for long periods you will find that it gets hidden in a longer AHT figure, and agent burn out happens.
  10. Call Abandons are calculated using the Erlang A formula, which assumes an Average Patience -also know as Average Time to Abandon (ATA).
  11. The Calculator can deal with up to 10,000 agents, thanks to some help with the maths from Philip Wright CEng – (Former Technical Director & CTO Europe at Aspect Telecommunications/Communications 1988-2001).

Need To Include WebChat And Emails?

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Terms and Conditions

Use of the Erlang C Calculator is subject to our standard terms and conditions.