With the first quarter about to end, analysts are tossing around possible sales figures for Apple's iPad.

Apple's tablet

A group of analysts questioned by Fortune are estimating unit sales anywhere from 5 million to 8.8 million.

Their estimates cover the period from January 1 through last Saturday and include sales of both the iPad and iPad 2. On average, the 31 estimates point to unit sales of more than 6 million iPads in just under three months. The estimates were also gathered at various times, with most of them coming out this month but a few being offered in January before the iPad 2 hit the market.

The analysts didn't specifiy how their estimates were divided between the original iPad and the iPad 2. But the time period covered by the new iPad 2 includes just two weeks' worth of sales in the U.S. and about two days' worth across much of the rest of the world. The sales estimates also should be seen in light of the iPad2's inventory challenges in which many consumers trying to get the new tablet in the stores have left empty handed and those ordering online face a wait time of three to four weeks at this point.

The huge recent demand for the iPad 2 also means that some of the estimates may end up being on the low side. J.P. Morgan analyst Mark Moskowitz told CNET News that the 6 million in unit sales his firm forecast for the first quarter is a bit "stale" with the release of the new tablet.

"Having seen the device and seen the great traction out of the gate here, I think one has to assume that there's probably some upside potential to that number," Moskowitz said. "It's just amazing that these guys come out with their new product, and they have lines that wrap around the block."

The analyst also offered his thoughts on why demand for iPad 2 has so dramatically outstripped supply. Though part of it is probably calculated on the part of Apple, according to Moskowitz, overall demand has just been much better than anticipated. Also, Apple has run into difficulty in the past keeping up with demand for such items as the iPhone. And ramping up enough inventory is especially hard with a new product like the iPad 2.

Looking at some of the upgrades in the iPad 2, Moskowitz pointed to challenges on the supply chain side getting the components out the door fast enough.

"These are new features based on components that are not really mature in terms of the supply chain," Moskowitz said. "This is all new type of technology, and the supply chain is not really mature in terms of the economies of scale."

In a March 22 research report, Moskowitz estimated that Apple would ship 29.2 million units. Though he's sticking with that figure for now, he said there is probably some upside to that number, especially if the strong demand for the iPad 2 continues into April and the next quarter.

Looking at the iPad 2 alone, Apple may have sold anywhere from 400,000 to 500,000 units during the tablet's first weekend of sales more than two weeks ago in the U.S., according to Piper Jaffray analyst Gene Munster. But given that most stores had sold out by that Saturday, those numbers could be seen as a one-day total--or even less than a day since the tablet didn't go on sale until that Friday afternoon.

In an informal survey of iPad 2 buyers waiting online, Munster's research team also found that around 70 percent of them were brand new to the tablet, with only 30 percent upgrading from the original iPad.

Updated at 9 a.m. PT with Mark Moskowitz's comments.