The quickest and easiest way to measure your Organic Reach is by looking at your posts on your Facebook Page. The post above had an “Organic” reach of 3,918 people. Again, this is the total number of people — fans & non-fans — who saw the post. (Non-fans see posts when a friend Likes, Comments or Shares your post)
https://www.postplanner.com/how-to-measure-increase-facebook-reach/

