How many trunks do I need for my inbound call centre?

The rule of thumb for calculating the number of trunks
(telephone channels) needed in an inbound call centre is:


The number of trunks is equal to the number of concurrent agents active in the call centre multiplied by 1.2

But like all rules of thumb there are a few assumptions:

  • All calls are being handled by your people (live agents) – if some of your calls are being handling automatically via an Interactive Voice Response (IVR) then you will need an additional trunk for each IVR port.
  • Your call centre is delivering a good level of service – the rule of thumb assumes that you are answering callers promptly (for example answering 80% of calls within 20 seconds or better). If your call centre is not answering calls effectively then you need more trunks.
  • Calls are handled completely within the call centre – if your agents need to transfer calls out of the call centre then additional trunks will be needed to support the transferring function.

But I don’t know how many agents I need in my call centre!

Our rule does assume that you know how many agents that you have or need to handle your calls efficiently.

If you don’t now the number of required agents then there are tools for inbound contact management planning in the Call Centre & Resource Planning section of our web site.

You can read more about our inbound contact management software here. Or why not contact us to get more help with your plans?


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Please note that this website is not offering specific advice based on your circumstances. We aim to provide you with information based upon our general contact and process management experience. If you are unsure about any information provided here please contact us for advice.