The Medium Rectangle (300×250) ad is a high-performing unit designated for placements in the sidebar on desktop and tablet or in-content on desktop, tablet, and mobile. If enabled, this ad size can display as a Pillar ad located in one of the corners of the page. If an ad unit has Flex technology enabled, it will also appear in rotation with a Half-page (300×600) and a Wide Skyscraper (160×600).
Advertisers have the most demand for this ad size and because it can be used across all devices it is a very popular ad.
