The iPad is one of Apple’s top selling devices and there is no sign of that momentum slowing down anytime soon. One analyst raised sales figures for the iPad and said he expects the device to join the iPod at Target stores. Piper Jaffray Senior Research Analyst Gene Munster raised his iPad sales estimates for 2011 from 14.5 million to 21 million units. Munster’s estimates are based on three factors.

The first is increased supply and an expanded distribution channel. Munster sees the supplies of the iPad increasing as Apple increases capacity of its manufacturing. He also believes that over 1,000 U.S. Best Buy stores will carry the iPad by the end of September.

Calling the iPad the “Mac for the masses” Munster also said he expects Apple to start selling the iPad in Target stores before the 2010 holiday shopping season gets into full gear.

Another factor raising iPad sales estimates is Apple’s international rollout. The device is now available in 20 countries worldwide, further expanding its reach. Finally, Apple’s move into the enterprise market with the device with the iPad is a positive sign for adoption, according to Munster.

“We believe the iPad represents a meaningful product category for Apple as a secondary computing device for those who already have a primary computer, a primary device for those who could not previously afford a Mac, and the first Apple product that will be a success in the enterprise; we see the iPad as the Mac for the masses,” said Munster.