Microsoft has released a very helpful tool in estimating the network bandwidth used by the different set of clients. It is an excel file like the storage calculator.
It is coded for both on-premise and Office 365 deployments. This tool will be of great help for companies that want to move to the cloud solution, but are not sure about the bandwidth requirements to have a decent connection with the cloud mailboxes.
As expected, it has a few fields where admin input is required.
The snapshot below shows the type of output you can expect.
Download the calculator here