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.
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.