Facebook Page
Engagement rate = (post|actions + post reaction|actions + comment|actions) / reach * 100;
Instagram
Engagement rate = engagement / followers * 100;
Engagements = retweet_count + favorite_count;
Engagement rate = engagements/followers/new_tweets*100
Twitter Ads
Engagement rate = (engagements / impressions) * 100
Linkedin Ads
Average Engagement = (clicks + (total_engagements - clicks)) / impressions * 100