The Erlang C Formula


Call Centre Helper’s Editor Jonty Pearce explains the Erlang C Formula.

What Is Erlang C?

Erlang C is a formula that works out the probability that a call has to wait to be answered.

The formula was originally developed by the Danish mathematician AK Erlang, hence the name Erlang, over 100 years ago.

It is particularly well suited to call centres as it allows you to work out the number of staff that you need for a given number of calls and a desired service level.

The mathematics is quite involved, this is what the Erlang C formula looks like.

Luckily there is an easy way to do this and that is to use an Erlang Calculator.

You can find one on the Call Centre Helper website. Just hit the Erlang tab.

You just enter in the number of calls – for example 100 calls per half hour.

You put in the average handling time (that is the talk time plus the time to process any post-call paperwork) for example 300 seconds, and a desired service level – in this case we use 80% of calls answered in 20 seconds.

So, in this case you will need 30 agents to handle these calls.


If you are looking for more great video insights from the experts, check these out these videos next:

Author: Jonty Pearce
Reviewed by: Robyn Coppell

Published On: 15th Aug 2022 - Last modified: 15th Nov 2023
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