Update: My meager math skills strike again, sorry. I've updated this to include Apple's retail sales.

Last week, there were preliminary reports from IDC and Gartner suggesting that Apple's share of the US personal computer market in the third quarter of 2007 was as high as 8.1 percent.  These reports were untrue. In fact, Apple's market share in that time period in the US was likely much less than that, and much closer to the 6.3 percent cited in other reports.

Now that Apple has released its financial results for the quarter, we can compare its numbers with quarterly estimates from IDC and Gartner. Long-time Internet Nexus readers are familiar with this process: What I do is average the IDC and Gartner numbers to obtain reasonably accurate worldwide and US sales numbers for the quarter. Then I look at Apple's numbers and see what percentage the Mac accounted for both worldwide and in the US.

According to Gartner, PC makers sold 68.5 million PCs in the quarter. IDC says the figure is 66.85 million. The average of those two figures is 67.68 million.

According to Gartner, PC makers sold 16.6 million PCs in the quarter. IDC says the figure is 17.9 million. The average of those two figures is 17.25 million.

Apple says it sold 2.16 million Macs in the quarter worldwide. That places its worldwide market share at 3.19 percent.

US market share is a bit more complex to compute. As it turns out, Apple doesn't provide US-only numbers. It did report, however, that it sold 965,00 Macs in the Americas, which I assume is all of North and South America, plus 473,000 units a retail worldwide (most of which were likely in the US given the mix of Apple's stored). Overall, the US is probably a big chunk of all that (60 percent? 75?). If the US were all of it, Mac market share in the US would have been 8.3 percent, or about the same as 8.1 percent figure that was bandied about last week. However, it's likely much less than that. For example, 75 percent of 8.3 percent is 6.25 percent. My guess is that's much closer to reality. I wish Apple would just break out US figures and settle this.

As for the other PC makers, here's how the top five came out both worldwide and in the US, from a ranking perspective:

Worldwide
1. HP
2. Dell
3. Lenovo/Acer (tie)
5.Toshiba

US
1. Del
2. HP
3. Apple
4. Toshiba
5. Gateway