The only way to truly calculate the dimensions is to fully parse the model. If there are tools that do this in a way that can be used from another program, I'm unaware of them.
Once you have the dimensions in LDU, you can easily convert to inches or centimeters. (See here.)
You can't calculate the dimensions in pixels. There's no sensible definition for that. You can determined the screen's DPI and then use your inch/cm value and convert, but I think that would be confusing more than anything, unless your goal is simply to draw something on-screen at actual size.
Once you have the dimensions in LDU, you can easily convert to inches or centimeters. (See here.)
You can't calculate the dimensions in pixels. There's no sensible definition for that. You can determined the screen's DPI and then use your inch/cm value and convert, but I think that would be confusing more than anything, unless your goal is simply to draw something on-screen at actual size.