Once more, Wall Street is betting Apple's iPad outsold domestic PC makers.

According to new analyst estimates compiled by Fortune, Apple (NASDAQ:AAPL) sold at least 14.8 million and as many as 23 million tablets during the calendar's third quarter, which happens to be the Mac maker's fiscal Q4. Apple reports earnings next week.

Fortune surveyed 61 analysts, 31 of which hailed from traditional Wall Street firms. On average, the pros pegged Apple's iPad sales at 17.6 million in the quarter that ended Sept. 29. The independent analysts put the total 9% higher, at 19.23 million. According to Fortune, the average of all estimates came in at 18.38 million iPads, which amounts to about 1.8 million to 3 million units more than the total PCs sold during Q3, going by data compiled by Gartner and IDC.

Either way, the introduction of lightweight Ultrabooks doesn't seem to be impacting iPad sales nearly as much as some expected. Dell (NASDAQ: DELL) sold just 3.3 million computers in the U.S. last quarter. Hewlett-Packard (NYSE: HPQ) sold about 4.2 million units over the same period.

Whether this marks the beginning of a permanent shift away from classic computing systems isn't entirely clear, though Microsoft (NASDAQ: MSFT) has taken steps to appease tab enthusiasts who don't exactly want to let go of the PC paradigm. The new Surface tablet, due next week, includes an option to purchase a fully functional keyboard for using the device like a lightweight laptop.

Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team and the Motley Fool Supernova Odyssey I mission. He owned shares of Apple at the time of publication. Check out Tim's web home, portfolio holdings and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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