According to a new study from market research firm NPD, 12 percent of all U.S. households own a Mac. That’s a pretty big increase for Apple, moving up 3 percent from the 9 percent of U.S. households reported for Apple in 2008. Here’s another interesting statistic that came from the report: of those 12 percent, almost 85 percent also own a Windows-based PC.

In fact, 66 percent of Apple households report owning three or more computers. Only 29 percent of Windows-based households own three or more computers, according to NPD.

The discrepancies aren’t limited to desktop machines. According to the report, 72 percent of Apple households own a notebook, while only 50 percent of Windows households own a portable computer.

Moving away from computers, NPD says 63 percent of Apple households own an iPod, while only 36 percent of all computer owning households report owning one. The same holds true for navigation systems, as well — 50 percent of Apple owners have some type of navigation system, compared to 30 percent of all computer households.

Stephen Baker, vice president of industry analysis for NPD, says Apple owners are more affluent, too. “Thirty-six percent of Apple computer owners reported household incomes greater than $100,000, compared to 21 percent of all consumers,” said Baker.

According to Baker, the average Apple household owns 48 consumer electronic devices, compared to 24 for the average consumer household.