According to Facebook, impressions are the number of times a post from your Page is displayed. People may see multiple impressions of the same post. For example, if someone sees a Page update in News Feed and then sees that same update when a friend shares it, that would count as 2 impressions.
Reach is the number of people who received impressions of a Page post. Reach might be lower than impressions because one person can see multiple impressions. For example, a person who sees multiple impressions would represent a reach count of one. [Source link]
When a user posts directly from our sharing station to Facebook or Twitter, we’re able to gather the number of friends and followers a person has. According to XYZ, social media posts receive impressions from roughly 30% of a person’s friends/followers. Therefore, a simplified example would be if Facebook user has 100 friends and posts, we can say that 30 of their friends will see the post. That would mean this one post to social media has an estimated reach of 30. While exact numbers will vary from platform to platform, the same can be applied to Twitter.
Email and Text impressions are calculated based on the expected behavior of a person who shares a photo from our social media sharing station via e-mail. From our years of experience, we know that at live events many users email the photo to themselves and then post to social media directly through their own devices. Since these users did not use our sharing station, we are unable to gather exact friend/follower counts. Therefore we use the industry standard median of friends a person has, as calculatged by PEW Research Center [Source link]. We then use the same method of calculating as outlined above. We are confident that if a person shares a photo via email, they have shared it to social media and that an average of 101 people may have seen the photo. Thus, an email share has created 101 impressions.
The instagram API does not allow us to record the exact number of followers an Instagram user has. According to Mike Byrne of Optical Cortex Reports, the average number of instagram followers is between 843 and 194 [Source Link]. For our calculations we opt to use the lower number of 194 as our user’s follower count. Thus each post to Instagram will generate an estimated 58 impressions.
To calculate overall impressions we simply add up the total of impressions calculated in each share category. For example, 100 email impressions, 100 Facebook impressions and 100 Twitter impressions would yield an estimated 300 total impressions.