1- Login to Webmasters Tools.
2- Move to Health Tab.
3- Move to Index Status.
4- Click on Advanced.
5- View the number of pages blocked by robots.txt.
Also See:-
Google Tag Manager
Google Adwords Bidding
Multi Channel Funnel in Google Analytics
Regular Expressions on Google Analytics
Backlink Watch
Seo Powersuite
New Crawl Error Alert Feature in Google Webmaster Tool
Rich Snippets in Google
Google Knowledge Graph
Google Search Tips and Tricks
Stop Words in Seo
Google Search Tips and Tricks