The number of devices shipped globally is expected to grow from 2.37 billion in 2014 to about 2.5 billion this year and further to 2.57 billion in 2016, Gartner said in a statement.
According to its estimates, worldwide tablet sales will reach 233 million units in 2015, an 8 percent increase from 2014 as demand for tablets continues to be slow this year.
After a troubled year in 2014, global tablet market is not returning to the levels of growth seen in the last four years, Gartner said in a statement.
"The collapse of the tablet market in 2014 was alarming. In the last two years, global sales of tablets were growing in double-digits," Gartner Research Director Ranjit Atwal said.
He added that the steep drop was on account of lifetime of tablets being extended and lack of innovation in hardware, which refrains consumers from upgrading.
The mobile phone segment is expected to grow 3.7 percent in 2015 to reach 1.9 billion this year from 1.83 billion last year.
"The smartphone market is becoming polarised between the high- and low-end market price points. On one hand, the premium phone with an average selling price at $447 in 2014 saw growth dominated by iOS, and on the other end of the spectrum you have Android and other open OS phones' growth area in the basic phone segment, where the average phone costs $100," Gartner Research Director Annette Zimmermann said.
For the mid-range smartphones, the market opportunity is becoming increasingly limited, Zimmermann added.
"From 2015, we expect Windows to grow faster than iOS, as the PC market stabilises and the challenge for the next iPhone to find significant growth becomes greater, narrowing the gap between the two operating systems," Atwal said.
The PC market (desktops and notebooks) is estimated to grow about one percent in 2015.