• by Erik Sass  @eriksass1, February 14, 2011

Tablet computer sales will increase more than tenfold in the next couple of years, according to two new forecasts that predict tablet sales making up an increasingly large percentage of overall computer sales.

Although Apple iPad sales will continue to increase, both forecasts predict that PC tablet computers -- especially those using the Android operating system -- will take more and more market share.

NPD Group's DisplaySearch division predicts that total annual tablet PC sales will soar threefold from around 19 million in 2010 to 55.7 million in 2011, then another 209% to reach 172.4 million by 2014. By then, tablet and slate-style computers will make up about 35% of the total PC market (forecast to reach 503.8 million by 2014).

Separately, iSuppli predicts that annual tablet computer sales, including the Apple iPad, will increase 1,110% from 19.7 million in 2010 to 242.3 million in 2015. Sales of media tablets (with more limited functionality than PC tablets) will jump 1,060% from 17.4 million in 2010 to 202 million in 2015.

Tablet computers with full PC functionality will increase 1,600% from 2.3 million in 2010 to 39.3 million in 2015.

Although the time frame covered by these two forecasts varies by a year, both clearly expect a huge increase in tablet sales, to around 200 million per year by 2014-2015.

Tablet sales have already increased almost tenfold in their first two years on the market, led by the iPad, up from under 2 million in 2009.

Competing devices will make up a larger proportion of sales, with iPad shipments dipping to less than 50% of total shipments by 2013.