Free apps are set to dominate download totals on smartphones and tablets in 2012, according to analyst firm Gartner’s latest forecasts for the industry.

The company claims that the number of downloads will top 45.6bn this year, up from 24.9bn in 2011, with 89% of this year’s total being free. Meanwhile, of the 5bn paid app downloads in 2012, Gartner reckons 90% will cost less than $3.

Gartner also estimates that Apple’s iOS platform will account for more than 21bn app downloads in 2012, up 74% year-on-year.

However, it sees Android’s Google Play and Windows Phone’s Marketplace as significant players going forward, as well as Amazon’s Appstore, Facebook’s App Center and – in China – a host of independent Android app stores.

Finally, Gartner sees in-app purchases continuing to grow, from 10% of app revenues in 2011 to 41% in 2016.