Reach vs Impressions: What's the Difference?

Reach is the number of unique people who saw a piece of content at least once - one person counted once, no matter how many times the content crossed their feed.

Impressions is the total number of times content was displayed, counting every view from every person, including the same person seeing it multiple times.

Because of that, impressions is always equal to or greater than reach for the same piece of content, and the gap between them is informative in its own right. A post shown to 500 unique people that generates 2,000 impressions means the average viewer saw it roughly four times - which can be a sign of strong algorithmic distribution, a highly engaged following that revisits content, or simply enough time in-feed for repeat exposure. Reach is the metric to track when the goal is broadening audience - how far a message travelled - while impressions matters more for judging whether repeated exposure to the same audience is building frequency and recall, which is why the two are reported together rather than as substitutes for one another.