Spoiler alert: It's not a lot.
According to an annual financial filing with the U.S. Securities and Exchange Commission, Microsoft has made $853 million (about £559m, AU$943m) from Surfaces. The figure accounts for both the RT and Surface Pro.
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No matter how you cut it
Apple, meanwhile, sold 14.6 million iPads in three months.
Comparing Apples and Surfaces aside, Windows tablet revenue was less than the recent $900 million (about £585m, AU$971m) write-down Microsoft incurred when it dropped prices of the RT.
To make the burn sting a little more, the Softies noted in the filing that Windows sales and marketing expenses grew to $1 billion (about £65.6m, AU$1.1b) for the fiscal year.
The 34 percent jump reflected "an $898 million increase in advertising costs associated primarily with Windows 8 and Surface." That's around £589 million/AU$993 million spent, or again, less than was made with W8/WRT tablets.