Height = CM instead of Pixels

[LogicalDohnuts]

Hey there, I'm using code to print out a document which is a CD Cover, now I've found that the code I'm using is basically working off Pixel dimensions which I can't afford to use, I'm wanting to use 12.1cm like so.

            Dim rect As RectangleF
            rect = e.Graphics.VisibleClipBounds()
            rect.Height = 12.1
            rect.Width = 12.1

But obviously you can tell what it's gonna do, it prints a tiny square of it . Now does anybody know how to make it so I can use CM instead of Pixel dimensions, I'd give it a shot but I'm crap at coding math, I figured I might give this a go

12.1 * 567

But sadly, that printed one huge image of it and I didn't want that. So does anybody know how to use Cm's instead of Pixels?

Thank you.