Reach

Reach is the count of unique users a piece of content was shown to. Different from impressions: one user seeing your post three times counts as 3 impressions but 1 reach.

Reach is the more honest top-of-funnel metric. Impressions can be inflated by people scrolling past the same post repeatedly or the algorithm re-serving content to engaged followers. Reach tells you actual audience size.

Most platform APIs return both. When optimizing for awareness, reach is the target. When optimizing for frequency (an ad campaign that needs to be seen 3+ times before conversion), impressions matter.