This Autodesk Knowledge Network Article lists the Build Number for Autodesk® Revit® versions from 2012 through 2016, Update 1 for R2. I expect the article will be updated with any future updates/service packs for 2016 (and beyond).
The Build Number can be determined by selecting the About Autodesk Revit 20xx item on the Help drop-down list found at the upper right corner of the Revit window. Select the right portion of the Help split button (with the down arrow icon) to deploy the drop-down list.
The Build Number is located in the upper right corner of the About Autodesk Revit 20xx dialog.
(Click on any image to see a full-size version.)