How to get physical size of window

Is there some more or less robust way to get (on mobile at least) the physical dimensions of the drawing surface?

something like graphicsdevice.width * deviceDPI

I want to render a sphere that is exactly 1 real-world cm in diameter on any screen.

This is more of a browser/front end centric question . Stackoverflow has some interesting replies

So then, if I query graphicsDevice.width, is the width reported in device independent CSS pixels? If no, how would I get them?