12th April 2022

Written by Jonty Pearce
Hi, I want to calculate FTE based on an ASA of 180 Seconds.
Is there a formulae for that.
The usual calculator would not answer it.
Question asked by Varun
If you want an average speed of answer of 180 seconds, then use a service level of 50% of calls answered in 180 seconds.
With thanks to Jonty
What will be the formuula?
With thanks to Triccia
It is the Erlang C Formula.
But the maths can get quite involved.
With thanks to Jonty
Author
Jonty Pearce
Jonty Pearce walked into his first call centre in 1989 and has been hooked ever since. He founded Call Centre Helper in 1989.
He is an Engineering Graduate with a background in marketing and publishing. In 2020 he won the AOP Digital Publishing Award for The Best Use of Data.
He writes and speaks on a wide variety of subjects - particularly around forecasting and scheduling. His in depth knowledge of forecasting algorithms has earned him the nickname "Mr Erlang."
Connect with Jonty on LinkedIn
Read more by Jonty PearceThe Latest Customer Contact Research, Reports and White Papers straight to your inbox!
Get the latest insights from Call Centre Helper by signing up for our email content.
24th September 2025
From Insight to Impact: The Next Era of CX and AI Leadership – Webinar