With VoIP there are three main things that you need to look at:
Upload Speed of the internet connection; the faster the upload the more concurrent calls the connection can handle.
Latency back to the hosted PBX; the lower the latency the better however, so long as it's under 100ms VoIP, calls should be fine.
Packet loss on the connection; if the connection is unstable and is dropping packets this will have a direct impact on call quality.
So how much bandwidth does a call use? Well this will depend on the codec being used, however, as a basic rule of thumb, a standard VoIP call with the default codec will run at 90Kbps, but can be as low as 30Kbps if the highest level of compression codec is being used. See the table below:
Codec Compression Level
64Kbps (kilobits per second)
8Kbps (kilobits per second)
In order to calculate how much bandwidth vs concurrent calls we recommend a simple calculator located at