According to the data, tablet sales will more than double in 2011 from 10.3 million units sold to 24.1 million units. In 2012, the numbers could reach as high as 35.1 million units sold. "Of those sales, the lion's share will be iPads, and despite many would-be competitors that will be released at CES, we see Apple commanding the vast majority of the tablet market through 2012," Forrester analyst Sarah Rotman Epps wrote in a blog post accompanying the forecast.
The Forrester data suggests that by 2015, tablet sales could reach 44 million units, and that the number of tablet users could be as high as 82.1 million. Epps explains,
The replacement rate (for tablets) will be closer to that of MP3 players or iPhones than to that of PCs. [...] Although they are certainly used for productivity, tablets are proving themselves to be lifestyle devices at home and at work, and as such we think consumers will upgrade to newer models more rapidly than they would a more utilitarian device like a PC. In other words, we think a significant number of first-generation iPad buyers will buy iPad 2 when it comes out this year--many first-gen iPads will end up entertaining the kids in the back of the car while Mom and Dad get the shiny new (likely Facetime-compatible) model.
Take a look the chart (below) showing the tablet market forecast for the next half-decade, in terms of sales figures and number of users.