How BIG is Exchange UM Voicemail?

After Googling this one “stukkend” (my SA buddies will know what I mean), I finally resorted to making a number of calls to get down to the actual atatchment size – cross referenced that with the math and came up with the answers.

Firstly it is worthy of note that the actualy size will depend on the following three factors:

  1. the message duration
  2. the audio codec used
  3. the audio storage format

UM uses either WMA, GSM 6.10 and PCM for creating the voicemail files.
WMA is always delivered as a .wma file and the GSM and PCM is delivered as .wav

Comparing the formats.


Bytes per 10 seconds

30 Second

60 seconds




156 KB

937 KB

Highest Quality, largest file size



48 KB

96 KB

Widely supported




39 KB

65 KB

Most compressed. The WMA format has a much larger header section than WAV (about 7K compared to less than 100 bytes) WMA files become smaller than GSM from 15 seconds and up.

The bottom line…
I generally use GSM since not all devices and apps support WMA. Usually I allow for approximatly 100 KB per minute of voicemail.
Now for the tricky bit, how much voicemail to cater for?
According to Forbes (and chatting to many folks over the years…) the average person gets around 2 voicemails per day. Most voicemails are around the 30 second mark in duration (or less)
Calculation is thus approximatly 1 minute of voicemail per day per user.

Using GSM, thats about 100 KB per day per user, 3 MB per month for each user and thus 36 MB per year.

Is that all? On average yes…there are exceptions, very LARGE ones as this is based on users who actually attempt to answer calls.


About Paul B

My name is Paul Bloem and I am employed at Lexel Systems in New Zealand as a Principal Consultant for Unified Communications. I have been working on enterprise voice solutions for over 20 years. My first 10 years were spent working for a Telco in South Africa (Telcom SA). This is where all the groundwork happened as I was exposed to just about every aspect of telecommunication you could imagine. I develop an interest in PBX technologies and eventually became the go-to guy. Next, I had a 10 year run at Siemens South Africa, most of my time there was as a Technical Trainer. During this time VoIP hit the world stage, I had the privilege of introducing VoIP both as H.323 and later SIP across the Siemens HiPath 4000 solution stack. In 2008 I immigrated to New Zealand with my newly attained MCSE, I was ready to go where no PBX Techie had gone before. I was employed to explore OCS 2007 and that was pretty much the beginning of the end for me. I have been working on OCS and Lync ever since. My current role focuses exclusively on Lync and associated technologies.. That includes pre-sales, consulting, architecture and design, training and support. I even get to play in the development space from time to time - focus on play ;-) I was nominated as a Microsoft VTSP for Lync early in 2013 and also awarded Microsoft's MVP award for Lync in 2014.
This entry was posted in Exchange UM 2010, How BIG is Exchange UM Voicemail?, Lync and UM 2007, UM, Unified Messaging. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s