As of February 1, 2016, the method for calculating the HTML5 ad size follows the preliminary guidance of the IAB for ads with and without additional assets.

Calculating Size for Ads with Workspaces Only

Assets that are counted towards the ad size include images, videos, fonts, JavaScript files, HTML files, and any other file type found in the Workspace. If there is more than one video in the Workspace, the calculation includes only the largest video.

The size of an HTML5 ad equals the total size of all assets in the ad’s compressed Workspace.  Compression is automatically applied, reducing the size of each asset type to the compressed size.

For example, if an ad includes five images, three videos, one HTML file and two JavaScript files, its size is calculated by adding the compressed sizes of the five images, a single HTML file, two JavaScript files, and only the largest of the three videos.

Calculating Size for Ads with a Workspace and Additional Assets

Ads that contain additional assets are calculated exactly as ads with Workspaces only; however, there is one exception. If the ad has an additional asset that is larger than the largest video in the Workspace, that asset is included in the calculation instead of the largest video.

The following table describes how ad size is calculated according to the different ad types. 

Ad Type Ad Size Calculation
Regular ads with no videos The ad size is the size of the Workspace and the largest Additional Asset (if one exists).
Rich Media ads with a video All the ad’s non-video assets, plus the largest video in the Workspace. If there are additional assets, and one of them is larger than the largest Workspace video, it will replace that video in the calculation.
Dynamic Creative ads The ad size will be the sum of the ad's non-video assets, plus the largest video in the Workspace.
Important: Sizmek continues to apply the old calculation method to the following two scenarios:
  • Ads that were created before February 1, 2016 are counted according to the old calculation method, whether or not they are attached to a campaign.
  • When ads that were created before February 1, 2016 are copied to create new master ads, the resulting master ads are counted according to the old calculation method.


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    Could we please make this page visible to clients ASAP due to the large number of requests/issues around the new file size methodology?

    I noticed this page has just been updated with some detail removed. We need a resource we can link clients to explaining the changes and recommendations on how to proceed and how to estimate file size. It looks like not all clients saw the email memo or was picked up by their spam filter.

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    Robert M Hall

    Also - could there be a clarification or additional information added to clarify wether or not shared JavaScript libraries like Greensock GSAP, CreateJS, and a few other select JavaScript libraries (reference: ) are to be included in the weight calculation, and if that depends on wether or not they are included directly in a workspace or linked to/pulled in from either Sizmeks CDN or external CDN's. There was an email that went out from Sizmek today with some of this information, and this detail was omitted, and questions are arising from clients and advertisers, etc.

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    Mark Newell

    Can we please have a generalized specification on how the compression will work? What percentage will be shaved off of images, video etc? I have quite a few clients asking about this. Obviously this will vary depending on the assets used, but I'd like to understand how this is calculated?