Reach refers to the total number of people who have seen your ad or content. If 100 total people have seen your ad, that means your ad’s reach is 100.
Impressions refer to the number of times your ad or content has been displayed on a screen. Let’s say that your ad from the previous example popped up on those people’s screens a total of 300 times. That means the number of impressions for that ad is 300.
Reach vs. impressions on other networks: Instagram treats “reach” and “impressions” almost exactly the same way that Facebook does. Reach refers to the total number of unique accounts that have seen your post or story. Impressions measure the total number of times users saw your post or story.
Snapchat treats “reach” and “impressions” slightly differently—it calls them “reach” and “story views.”
Google AdWords calculates two different kinds of reach: “cookie-based reach” and “unique reach.” The first measures unique users the traditional way, using cookies. Unique reach goes one step further by estimating and omitting duplicate views from the same user.
In Google Analytics, the relevant metrics here are “users” and “page views.” “Users” measures the number of people who have visited your site at least once during the relevant time range. “Page views” is the total number of pages viewed by all of your users.
