There are multiple ways to find the OWA 2013 patch or build level, one of those ways is check the OfficeVersion.inc file located here
You may also use PowerShell to get the same info by using
There are couple other ways to check the version number right from the browser without the need to log onto the WAC server itself. Please head over to my colleague Tom's blog post here.
not sure this works the way you are expecting. on several upgraded farms, I've checked this registry key and it is still set at the RTM version. so far the only reliable method I have been able to use is to look up the kb listed in "programs and features\view installed updates"
Agree with coolhand - installing SP does not change reported version
The script does not work if you installed WCA and then patched it! i have run this on 2 of my WCA farms with the March 2013 CU and it is showing the RTM version 15.0.4420.1017
It may work for slipstreamed installs but it doesn't give you the WCA patched version for upgraded WCA servers/farms.
Sorry, I didn't read coolhand's comment!
Run this command in Powershell to get version number.
Thank you all for your feedback, I have updated this post with more reliable ways to find the current WAC build number. Thanks to Tom S. and Joe Rodgers for their input.