Abstract: One or more systems and/or techniques for determining advertisement viewability are described herein. In an example where a webpage comprises a managed container within which an advertisement is populated, view percentage functionality associated with the managed container may be invoked to obtain a stream of viewable percentages of the managed container to determine a viewable percentage of the advertisement. In an example where the webpage comprises an unmanaged container in which the advertisement is populated, a grid may be generated and evaluated to determine a viewable percentage of the advertisement. When the viewable percentage of the advertisement is above a percentage threshold for a duration threshold a viewable impression beacon is generated for the managed container based upon the viewable percentage. The viewable impression beacon may be indicative of viewability of the advertisement (e.g., an amount of the advertisement that may be visible to a user).