A medium rectangle is the 300x250 pixel banner, the most common ad size on the web. It usually sits in the sidebar or inside the article text.
How it's sold
Most of the 394 publishers selling it run it on their own site, from Pubfinity to smaller blogs, and you book through their sales team, a self-serve form, or a DSP. It is one of the easiest sizes to buy programmatically.
What it costs
The median published rate is 950 USD per month, based on 14 rates. Where publishers sell it by impression, the median is 26 USD per 1,000 impressions.
What you supply
You supply one 300x250 image or HTML5 file, and many publishers also ask for a backup static image.
Best for
It suits traffic and awareness campaigns that need wide reach across many sites.
Before you buy
Look at the slot's position on the page, because a 300x250 above the fold and one at the page bottom perform very differently.