Publishers now have the option for their 1x1 widget(s) to automatically render within IAB's fixed ad unit sizing recommendations by adding the attribute data-banner-size to their widget's div. For example, if we were to specify:
data-banner-size="300x250"
The widget would automatically render in the following 300x250 format:
The following sizes are supported:
120x600
160x600
240x400
250x250
300x50
300x250
300x600
300x1050
320x50
336x280
640x1136
728x90
720x300
750x1334
970x250
970x550
1080x1920