Google says it's just as big in the red-hot app ad market as Facebook

Universal app campaigns, Google's tool that lets app advertisers spend across several services — and a pillar of Google's strategy to wrest dollars away from Facebook — are coming to Apple's iOS.

Google announced the news during its I/O developer conference on Wednesday.

More critically, the company also released some rare figures. Google's ads have driven over two billion total app downloads, the company said. And it got there thanks to the universal app campaigns ad tool, which lets developers promote their app across search, YouTube and Google's mobile ad channels. The tool doubled the app installs volume over the past year.

At its developer conference last month, Facebook said its app promotion products have driven two billion plus downloads, too. Facebook is often considered the go-to place to drive app downloads, but Google is now talking more openly about its performance.

Not every part of Google's tool will work for iOS apps — developers can't run ads in the app store, as they can on Android, since Apple doesn't do that.

Google is, however, adding a new channel: App developers can run ads inside Gmail later this year.