What are Erlang Formulas and how do they help call centres?

Erlang Formulas are a critical calculation to determine how many call centre agents you need to meet service levels.

And if you have spent any time in and around call centres especially in a Workforce Planning area there is a fair chance would have definitely heard the term.

But what is an Erlang formula and is it a friend or foe???

A super quick history lesson of Erlang Formulas

Back in the early 1900’s, when telephone calls were enabled by manually connecting two circuits together, the Copenhagen Telephone Company needed a way to find out how many circuits they needed to meet the demand, and how many telephone operators they needed to connect the circuits (any of this sounding vaguely familiar?).

Well, enter Mr Agner Krarup Erlang, a mathematician, astrologist, physicist and chemist who developed a mathematical formula to provide the answers.

The marketing budget was pretty tight back then (good to see some things never change) so rather than coming up with an elaborate name for the formulas Mr Erlang developed, he decided to go with Erlang A, Erlang B and Erlang C. Brilliant.

OK, this will really blow you away.

Those logarithms Mr Erlang developed are still the basis for determining the required number of agents to meet a forecasted demand in a call centre over 100 years later!

In short, Mr Elang was the original Workforce Optimisation Planner.

And sadly, yes, that was past tense, Mr Erlang passed away following abdominal surgery aged 51 on 3 February 1929.

Which Erlang Formula should you use?

When deciding which Erlang formula to use, the key deciding factor is what will happen when all your agents are busy handling calls.

Erlang A

Similar to the most popular formula used (Erlang C), Erlang A includes abandoned calls whereas Erlang C assumes there are no abandoned calls.

Erlang B

The quick explanation is that Erlang B is normally used to determine how many phone lines (aka trunks) you need.

Erlang C

The most widely used formula in determining how many staff you need to meet the required Service Levels.

Read this article to learn more specifically about Erlang C.

Erlang C Calculator Download

Want to work out how many staff you need to answer all the calls?

What about the impact of reducing staff numbers or your average talk time increasing?

Our free call centre calculator will enable you to model a range of different scenarios and we’ve included some easy instructions so you can play along.

Click here to learn more.