What is Reach?

Reach is the total amount of unique visitors to a post. Let’s say you have 10.000 followers on Instagram, but of these only 5.000 people see the content posted. Therefore, the reach here is 5.000.

Difference between reach & impressions:

Reach is the number of unique visitors who saw the content. Impressions are the number of times the content is displayed.

Example: I watch a video once - the reach and impression are both 1.

                  I watch a video 5 times - the reach is still 1 while impressions is 5 now.

Reach in a campaign

The reach you see in the reporting tool for a campaign is not the accumulated score of the reach of each post in the campaign.  

Example:

If one influencer publishes multiple posts to his followers (let's say 200k) then the overall reach and engagement is not the total score of all the posts. So, if the influencer publishes 3 posts for the same campaign, the total reach is not 600k (3x 200k), because he is reaching the same 200k followers with the posts.