Begin-to-render impression counting

Viewability standard

A viewable ad is one that actually was viewed. Advertisers consider this metric critical because it helps determine whether the ad had a chance to be seen by their audience. To ensure measurement is consistent and fair across the internet, industry groups like the Interactive Advertising Bureau (IAB) and Media Rating Council (MRC) set rules for how ad views are counted to help with making viewability reporting more consistent across the digital advertising industry.

MRC viewability

An impression is “officially” classified as viewable once half of the ad is visible on a user’s screen for a minimum of one continuous second. This baseline standard is the result of joint efforts by the IAB and the MRC, an American non-profit focused on reliable media reporting. For in-stream video ads, the minimum duration is two continuous seconds. Some large display formats may qualify under a 30% visibility threshold, depending on the applicable measurement methodology. Different user interactions may also count in specific circumstances, but a click should not automatically be treated as proof of viewability in every measurement system.

Active view impression

From February 17, 2027, Google Ad Manager and AdSense will change how they count display banner impressions on desktop, mobile web, and connected TV (CTV), moving from Count-on-Download (COD) to Begin-to-Render (BTR). It’s a step further, as BTR is already used in other inventory type cases:

• The old way (Count-on-Download – COD): Google counted an impression the moment the ad started downloading to a visitor’s device. It counted impressions even if the user quickly scrolled past or closed the page before the ad appeared on their screen;
• The new way (Begin-to-Render – BTR): Google will count an impression when the ad has successfully loaded and begun rendering.

Impression measurement methodology

The transition from Count-on-Download (COD) to Begin-to-Render (BTR) makes impression counting more rigorous by counting an impression later in the ad-serving process. Under the old ad impression measurement method (COD), an impression was counted as soon as the ad code downloaded, meaning it could be recorded even if the user closed the page before a single pixel ever appeared. BTR eliminates these impressions by only counting an ad when it actually starts rendering. While BTR does not guarantee that an ad is fully visible or meets the viewability threshold, it provides a more meaningful starting point for impression counting by confirming that the creative has begun to render on the user’s device.

From serving to seeing

• The Foundation (COD to BTR)
  Before you can measure viewability, you have to count the impression. Currently, COD counts this the moment code is downloaded. In 2027, BTR will tighten this by only counting when the ad starts drawing pixels;
• The Internal Verification (Active View)
  Google’s proprietary Active View technology measures whether an ad meets the IAB viewability standard: at least 50% of the ad must be visible for one continuous second for display ads, or two continuous seconds for in-stream video ads;
• The External Verification (OM SDK)
  The Open Measurement SDK (OM SDK) helps independent measurement companies check whether ads meet viewability standards. The results may vary depending on how each company measures viewability.