This is also valid for Exchange Online (Office 365)

http://blogs.technet.com/b/exchange/archive/2012/02/10/announcing-the-exchange-client-network-bandwidth-calculator-beta.aspx

I am extremely pleased to announce that the all new Exchange Client Bandwidth Calculator Beta is available for download!!

Over the past 12 months we have been working on a new calculator to help with Exchange client network bandwidth approximation. This new calculator is based on all new prediction data and is designed to work with both Exchange on-premises and Office 365 deployments! (Yes, we know it’s long overdue!)