How to scale/calculate GameObject Z distance to the real physical world...

Our application interacts with the physical world, and I suspect as more VR/AR apps are developed this will become a common question: How do I position an object in virtual worldspace so it is at a simulated distance comparable to real physical space? In other words, a 1 meter x 1 meter cube 10 meters away from the camera looks the same as a 1 meter x 1 meter physical cube 10 meters away in physical space?

I would assume the aspect ratio and measurement of the display's rectangle would have to be calc'd with the FOV, and Z value of the GameObject. But, before I attempt such, I was hoping somebody has already done this or at the very least some super smart math genius could suggest a formula.