Google Webmaster Tools - Subscriber stats
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See below for screenshot and explanation of Subscriber stats which is within the Your site on the web category.
Here are the Google webmaster tools categories as they look when you are logged in (left).
Webmaster tools - Your site on the web - Subscriber stats
Subscriber Stats is an interesting tool that has a few disclaimers regarding it's use on the help page (new window), I use feedburner but not for this website and apparently the feedburner subscriber data may not all show up on this tools list. I am not informed enough to gauge whether this is a good tool.
See the Webmaster tools Help page on "Subscriber stats" (new window).
Here is what a screenshot of the Subscriber stats category looks like in Webmaster tools (below).
Screenshots on this page are copyright © 2018 Google Inc.
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