Which ad sizes does Spaceback support?

We recommend the standard IAB ad sizes to maximize the availability of inventory, though technically Spaceback supports any ad size. The most common ad size is the 300x250 Medium Rectangle because it translates most closely to the Instagram 1x1 default aspect ratio. The second most common ad size is the 300x600 Half Page Ad because it translates most closely to the aspect ratio of most Pinterest pins and vertical oriented Instagram posts.