First iPad estimates: 4 million units in year one, 8 million in 2011

In a research report to clients, Piper Jaffray analyst Gene Munster said the iPad's $499 entry-level pricing now leads him to believe Apple will sell between 3 and 4 million of the devices in its first 12 months on the market. That's up from his earlier prediction of just shy of 1.9 million units made at the end of last year under the assumption that the product would average a $600 price tag.

"We have measured enthusiasm for the device's first year (2010), but we expect 2011 to be a breakout year for the iPad adding $4.6b (7.5%) to revenue in 2011," Munster said. "The iPad business may take one year to solidify, but we see it as an investable theme for shareholders given its impact on 2011."

Still, Munster believes his first-year figures may come in at the lower end of Wall Street's consensus estimates, which are expected in the 4 to 5 million unit range. However, his belief that the iPad is poised to generate Apple an incremental $4.6 billion in sales the following year would equate to a doubling of unit sales to 8 million in 2011.

The analyst, who was in attendance for Apple's hands-on session with the iPad shortly after its announcement, also took pause to assess the iPad's potential to eat into sales of it's much smaller cousin, the iPod touch. While he doesn't see the tablet affecting sales of Macs, he trimmed his 2010 iPod touch unit sales estimate by roughly 1.8 million units to 20.6 million.

"After using the iPad, we believe it will cannibalize iPod touch sales, but not Mac sales," Munster said. "The gadget is a premium mobile device, not a computer; as such, we see some iPod touch buyers stepping up to the iPad, but consumers looking for an affordable portable computer will likely stick with the MacBook lineup."

The analyst maintained his "Overweight" rating and $280 price target on shares of Apple.