The iPad officially became available for pre-order earlier today and while plenty of you are still debating about whether or not to pre-order, it appears as if the device might already sold 51,000 units in just two hours via pre-order. Wow.

If you’ve ever doubted how insane dedicated Apple fans are, the background on how these figures were determined will assuage any doubts. A group of particularly prudent Apple fans from the APPL Sanity Board at Investor Village decided to put together a spreadsheet of order numbers, times that orders were placed and contents of those order. As someone who has been known to obsess over Apple details myself (tracking a freightliner from China to the US with 27″ iMacs on-board in order to better guestimate delivery time), my hat is off to these folks!

Using this information, they were able to come up with a baseline for the number of items being sold through the Apple Online Store.

Fortune’s Phillip Elmer-DeWitt reports:

“51,000 orders in two hours,” announced Victor Castroll shortly after noon. He’s an analyst with Valcent Financial Group and an AAPL Sanity member who, with the blogger-analyst who calls himself deagol, has been monitoring the spreadsheet.

This matches other estimates from blogger Andrew Erlichson who wrote:

“We just bought two iPads, about 30 minutes apart. Our order IDs are 10,000 apart. Assuming those order IDs are sequential, and they appear to be, then Apple is selling 20,000 iPads per hour.”

Now as with anything unofficial, there are caveats — major ones — assuming that the order number system has been identified and “cracked” so to speak, this would really be more accurate for all orders placed through the Apple Store, not just iPad orders.

Additionally, these figures wouldn’t account for orders with multiple iPads (you can only pre-order two at a time). This also doesn’t include any reservations to pick up an iPad at a local store (no payment information is required for that and you aren’t given an order number).

Still, it’s safe to say that the majority of orders placed through the Apple Online Store are for the iPad.

I’ve reached out to Victor Castroll for a more recent update and will update the post if I’m able to get any more information.

Reviews: Apple Store

Tags: apple, ipad, ipad preorder