A wise man once said “you can never have too much money, coffee, or bandwidth.”

It’s one of those strange truths of networking. No matter how much bandwidth you buy, your consumption will increase to the point where it’s barely enough and you will want more. We’ve all seen this phenomenon, and as more of my customers are starting to move their Exchange to “the cloud” one of the things they need to plan for is how much bandwidth they will need.

While “the cloud” increasingly seems to mean Office 365, several of my customers are choosing to deploy their own Exchange servers in an IaaS environment, either Microsoft’s Azure or Amazon’s Web Services. Even if you’re just building a new datacenter, knowing how much bandwidth you need for your clients is critical, and there is little that is more critical to end-users all the way up to senior leadership than email.

And that’s where a great, if somewhat dated, tool comes in. The Microsoft Exchange Client Bandwidth Calculator is an Excel workbook that enables you to calculate just how much bandwidth you will need to support client access to Exchange. You simply download the workbook, enter the information for Exchange and up to four personas, which include variables (conveniently coloured in blue,) and drop down values (coloured red,) and then define up to 19 sites and the number/mix of clients you have. Finish that up and then viola!, you have an estimation of your bandwidth requirements related to client traffic.

There are a few things to note. First, this calculator is largely unchanged since 2012 and still bears the “beta” tag. That should not be overly concerning though, as it’s been proven out over the past several years by consultants world-wide.

Second, it does not cover Outlook 2013 or 2016. To be blunt, the bandwidth consumption differences between Outlook 2010 using Outlook Anywhere and Outlook 2016 using MAPI over HTTP are insignificant. Don’t worry about this either.

Finally, like any calculator, this one suffers from one small but critical flaw, which some of you will know as GIGO. GIGO is one of those old acronyms that means “garbage in, garbage out” and the Client Bandwidth Calculator needs valid input to give you reliable output. Guess wrong on any one of the many values that you must input to run the numbers, and odds are good the output is going to be way off. You are going to need to spend time researching your users and developing your baselines to be able to enter accurate values. What? You don’t have that much time to spare and you don’t have any baselines? Me neither. Don’t worry. There’s a great solution to this problem that we will blog about in our next post. Stay tuned!

You can download the Exchange Client Network Bandwidth Calculator from https://gallery.technet.microsoft.com/Exchange-Client-Network-8af1bf00  and there is a handy guide from the authors on how to use the calculator which you can download from https://gallery.technet.microsoft.com/Exchange-Client-Network-ea5eeb02. If you need to plan for upgrading existing circuits or provisioning new ones, and Exchange is in the mix, the Exchange Client Network Bandwidth Calculator is a must have tool for you!