In November 2016, the IAB also released an updated set of Guidelines that takes into account the evolving world of online advertising. This new specification focuses on using responsive design, and makes new recommendations in regards to expandable and other rich media ad products. The New Guidelines are expected to be officially released in 2017.
Ad-Server Specific File Size Limits
Ad-servers generally follow the size limits recommended by the IAB, although there is no standard way that those file size limits are enforced. Some examples of the specifications for different Ad Servers are:
If you are unsure of the file size limits for your ad server, we recommend that you check with a support contact at that ad server.