One of the most common advertiser questions in display relates to ad sizes. While there are many sub factors relating to ad sizes such as frequency capping, above/below the fold, ad format, rich media, etc., at its core, the ad size itself certainly is an important factor in any successful display campaign optimization.

The five most common Display creative sizes are:

-          120 x 600 (narrow vertical tower)

-          160 x 600 (wider vertical tower)

-          300 x 250 (box)

-          468 x 60 (small horizontal banner)

-          728 x 90 (large horizontal banner)

There are many other ad sizes as well, both smaller and larger but we will focus on the inherent performance and delivery differences of the main 5 ad formats.

Figure 1: EF US Client Ad Size Performance 2010

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Historically, there has been more display inventory on publishers’ sites in the 300×250 and 728×90 ad sizes due to that format working best with the general layout of publisher web pages. The EF data in 2010 would also support that notion, with 63% of all inventory coming from those 2 ad sizes.

These sizes also represent the ads that have the highest likelihood of being clicked by a browser as well which certainly speaks strongly as a major component of how an advertiser should optimally bid a given ad creative. The 300×250 and 728×90, along with the 120×600 narrow tower, also have the highest CTRs.

Now, this does not account for ROI for a given advertiser to their success metric or the “quality” or vertical of the publisher. The impact of view-throughs (where a consumer completes the advertiser’s conversion goal such as a lead or sale subsequent to being served and viewing a display ad but not actually clicking it) is also not encapsulated in this data.

The fact that 428×60 ads have the lowest amount of inventory and the lowest CTR should be balanced against the fact it is also the cheapest inventory to buy judging by EF’s 2010 data. At $0.39 CPM, it is just a bit over one-fifth of the price of the next cheapest inventory size in 2010 being the 728×90 ads.

For any advertiser wanting to optimize a display campaign successfully, they should not neglect any of the major ad sizes as having more options to display your creative will allow for greater efficiencies. It is important to note that if you have 5 different ad sizes, for each different message/product/special offer/display exchange, etc. that you are promoting, the number of bid/ROI permutations multiples very quickly.

Given this, for best results, as well as the ability to test different messages, a sophisticated algorithmic and cross channel  platform should be utilized so you are bidding optimally each day (and in the case of Real Time Bidding, each second).  Advertisers need to look at results across all your digital channels together, be it SEM, Facebook, etc. as most users are browsing across the Internet and marketing media spend should not be looked at in silos.

Chris Jacob