The medium rectangle measures 300×250 pixels and is the most universal display size: it fits text columns, sidebars and mobile feeds, every ad network serves it, and in Google Ads it is consistently among the sizes with the largest inventory. If you can build only one size, build this one.
The name describes the shape: a rectangle of medium size, called MPU for mid page unit in the British market because it first ran inside the article there. The IAB Universal Ad Package of 2003 made 300×250 a standard that publishers, ad servers and networks all keep to, and the dimensions have not changed since.
Where the size sits on the page, how much copy fits and what file size is usual is on the format page 300×250 in detail.
myfeedr builds the medium rectangle in every package, as PNG and JPG, as an animated GIF and as an HTML5 ad with the same design.
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Enter your address, myfeedr reads logo, colours and products and builds every size – free until you want the files.