Ad depth

Ad depth measures how many ads a results page carries. A page might show one sponsored listing, or several stacked in a block. Reports usually express it as the average number of ads per matched ad request.

Publishers have some say. In Google's Custom Search Ads, each ad block has a "number" setting for how many ads to request, with a default of two. What actually returns depends on how many advertisers are bidding and on the engine's own judgement about how many ads the traffic merits. Contracts and policies cap how many ads and blocks a page may hold.

More ads is not automatically better. Extra listings give the visitor more to choose from and can lift Ad CTR, but lower positions attract fewer clicks and usually cheaper ones. A page that is nearly all ads also draws the criticism levelled at Made-for-arbitrage sites and can breach rules on ad-heavy pages.

Watch depth together with coverage. Falling depth on a keyword suggests advertisers are leaving it, which often shows up before prices drop.

An example

Say a page requests 4 ads for "car insurance" and receives 4, but requests 4 for "vintage tractor insurance" and receives 1. Ad depth is 4 on the first and 1 on the second.