What Is an Ad Impression?

An ad impression represents the number of times an advertisement is delivered to a user’s device.

Each impression indicates that the ad was served—meaning the system attempted to display the creative material to the user—regardless of whether the user actually noticed it.

How Ad Impressions Are Generated

Ads can be delivered in two primary ways:

• Pulled ads – requested by the user’s browser when loading webpage content
  
• Pushed ads – delivered proactively, such as ads sent via email or notifications

In both cases, an impression is counted when the ad delivery system responds to the request and begins sending the creative to the user.

Technical Definition and Measurement

In a more formal, industry-standard sense, an ad impression is logged when an ad server records a valid response to an ad request made by the user’s browser. To maintain accuracy, the impression count:

• Is filtered to exclude bot or robotic traffic
  
• Is recorded as late in the delivery chain as possible, ideally at the moment closest to when the ad would appear on the user’s screen
  
• Reflects the opportunity to be seen, even if the user does not scroll or actively view the ad

This ensures the metric reflects genuine delivery rather than merely a technical request.

Delivery Methods: Server-Initiated vs. Client-Initiated

Server-Initiated Delivery

With server-initiated delivery, the publisher’s web content server manages the ad request, formatting, and redirection.

Impression counting in this model should occur after the server responds to the ad request—either at the publisher’s ad server or at the content server—to ensure accuracy.

Client-Initiated Delivery

In this model, the user’s browser is responsible for handling the request, formatting, and redirection needed to display the ad.
For client-initiated methods, impressions should be counted on the publisher’s ad server or a third-party ad server after the ad request has been made, or even later in the process.

Why Accurate Impression Counting Matters

Reliable impression measurement is critical for:

• Campaign reporting and billing, especially in CPM-based advertising
  
• Evaluating ad visibility and opportunities to be seen
  
• Detecting invalid or fraudulent traffic
  
• Understanding ad reach and optimizing placement strategies

Accurate impression data supports fair transactions between publishers, advertisers, and ad networks.

Relationship to Other Advertising Metrics

Ad impressions work closely with metrics such as:

• Clicks – user interactions with the ad

• CTR (Click-Through Rate) – the ratio of clicks to impressions

• Viewability – whether the impression was actually viewable by human eyes

• Conversions – actions users take after ad exposure

Together, these indicators help advertisers assess both exposure and performance.

Common use cases

301 redirects serve multiple strategic purposes in digital marketing. They’re essential when rebranding a domain, restructuring website architecture, consolidating duplicate content, migrating from HTTP to HTTPS, or removing outdated pages while directing traffic to relevant alternatives. E-commerce sites frequently use them when discontinuing products to redirect customers to similar items or category pages.

Implementation best practices

Proper implementation requires attention to several factors. Always redirect to the most relevant page possible rather than defaulting to the homepage. Avoid redirect chains (multiple consecutive redirects) as they slow page load times and dilute link equity. Monitor redirects regularly using tools like Google Search Console or Screaming Frog to identify and fix any issues. Keep redirect mappings documented for future reference during site maintenance.

Impact on user experience

Beyond SEO benefits, 301 redirects prevent frustrating 404 errors that damage user trust and increase bounce rates. They maintain continuity for bookmarked pages and external links, ensuring visitors always find working content regardless of how they accessed your site.

Learn more: Ad Network