The 120×600 ad unit is a now-defunct IAB standard ad unit historically referred to as a skyscraper. The skyscraper size was 120 pixels wide by 600 pixels tall. The 120×600 skyscraper ad size was retired in 2011 by the IAB.
The skyscraper ad size has now been changed to 160×600 (which is sometimes called a super-skyscraper or wide-skyscraper). The skyscraper size was changed due to the consistently bad performance of the 120×600 (due to being very small compared with the 160×600).
Whatever the skyscraper dimensions, it is generally placed on the side of a page so as to show to users an ad as they scroll down the page. This makes a skyscraper ad (of both types) somewhat immune to demands for above the fold placements.
This skyscraper ad size however still remains somewhat frequently in use so should not be ignored. It is now more commonly served through a multi-size ad slot with a 160×600 ad unit so that either ad size can appear in the same ad slot.
Both the skyscraper dimensions of 120×600 and 160×600 are less popular than 728x90s or 300x250s, yet should still be placed on every page of a site for incremental revenue.
What it looks like
The Skyscraper dimensions are 120 x 600 pixels. This is how large the ad unit is:
120×600 Ad Unit
(usually called a Skyscraper)
Here is an example of an ad that is this size:
120×600 Advice for Site Owners
You can generally expect a quite low CPM for this ad unit. However, it should not be rejected outright due to how common it still is. Add it to a multi-sized ad tag with a 120×450, 160×600 or 300×600 for incremental revenue.
This ad slot is often difficult to fill (whether using a 120×600 or 160×600) due to lack of demand, so having both options available is the best choice.
Tip: Placing CPA adverts in the skyscraper slot is a good idea, as they will ensure your users have cookies in place for post-impression sales.
120×600 Advice for Ad Buyers
We would not recommend using a 120×600 when building your own advertising. Salespeople will often try and convince ad buyers that this unit is good because it remains on a users page for longer. However, the performance does not support this view.
If the cost to you is minimal to create a 120×600 then we always recommend testing everything. You should find your own advertising sweet spot! In general, we wouldn’t expect this ad size to be a winner though.
Summary
Back: Ad Size Guide