3D World Scale?

I know the 3D features are very new, but are there any hints on what scale to use? Is there a standard, like the default 3D cube being equal to a meter/yard/other, or is it arbitrary?

My background is in 3D using real-world measurements so I feel a little strange ignoring it.

X and Y are pixels.

Z is about 5.7 times x/y at normal field of view.

There is a new expression on the 3D Camera plug-in: ZScale which can give you the proper scale for Z with various viewport sizes.