Total Engagement in Rival IQ is always the total number of engagement actions (reactions, comments, shares, etc).
We calculate Engagement Rate as the ratio of total engagement to a measure of the potential reach of the post. The reach number we use depending on if you're comparing public data or private data.
In the Competitive Public Data section (where we use publicly available data), we define Engagement Rate by Follower as the engagement total divided by the audience size at the time the post was made. This normalizes the activity between larger and smaller accounts.
In the Your Private Data sections, we provide multiple ways of calculating engagement rate to help you analyze how successful a post was. On Instagram, Engagement Rate by Reach is the engagement total divided by unique reach, while Engagement Rate by Impression is the engagement total divided by total impressions.
Engagement Rate by Follower is the sum of total engagement actions, divided by the sum of followers (or reach, depending on the section of the app). This normalizes the engagement rate between posts with on channels with more or fewer followers/reach.