Opinion: Flurry makes a confusing comparison between actual US online ad spend and potential US mobile app inventory

Continuing its number-crunching, mobile analytics outfit Flurry has been pondering the scale and growth of the mobile advertising ecosystem versus its internet big brother.

Although, apparently, that's not what the numbers suggest.

Building out from the 20 percent of the mobile ecosystem it reckons it tracks, Flurry has put together a graph which predicts the total available US mobile in-app advertising inventory could absorb the $12 billion-odd US online display advertising market by November 2011.

Of course, this is a somewhat slippery concept as the online number is the amount of money actually being spent now, while the mobile number is how much it would cost to fill every mobile ad that's available.

Indeed, as Flurry's Charles Newark-French points out himself, Gartner reckons the US mobile ad market in 2011 might be worth $700 million, while eMarketer goes for $1.1 billion. Obviously, neither is close to $12 billion.

The advertiser gap

The reasons are relative CPMs (something Newark-French discusses in the post) but mainly because mobile ad fillrates aren't very good (something he doesn't).

For example, according to ad aggregator Smaato, the average fillrate for a mobile advertising network in June was around 22 percent globally, or about 30 percent in the US.

Still, there are some significant numbers from Flurry's research.

It reckons the average mobile app session is 4.2 minutes, compared to under a minute for a website session. This enables mobile ad networks to show an average of 4.3 ads per sessions, hence driving the massive growth in mobile inventory.

As a mobile focused analytics outfit, Flurry's long been pointing out how the mobile app market is much more sticky than traditional advertising, something CEO Simon Khalaf stressed when we interviewed him a couple of months ago.

[source: Flurry]