I've been trying to sort this out over the weekend. All the macros available from searching goolge don't seem to work and have runtime errors and directx errors etc. I don't know how to program in Visual Basic, but I changed a couple of the macros I found, and now they work for me in SW2012.
First, draw a box 100mm square and then zoom the object to real size using View/Modify/Zoom in/out. Measure the part using Calipers or holding a rule up to your screen. Try to get this accurate to within a mm
Run the resolution.swp macro using Tools/Macro/Run to get your screen resolution. A box will appear with the number you need. <Capture1.jpg>
(If you use more than one screen this is screen specific and you need to make copies of the Zoom 1 to 1.swp macro edited for each screen, and assign them to different hotkeys.)
Edit the Zoom 1 to 1.swp macro with Tools/Macro/Edit and this will open the macro in Visual Basic. Modify the line: ModelView.Scale2 = 0.8625 to the number given from resolution.swp So in this case I would change it to ModelView.Scale2 = 1.455 to suit my screen. <Capture2.jpg>
Now try running the modified Zoom 1 to 1.swp macro to see if it works, and check your measurement on the screen. Modify the number again for fine adjustment if you want.
Next assign the Zoom 1 to 1.swp macro to a hotkey. I have mine set to Ctrl+M (for macro)
Go to Tools/Customize... Then select the Keyboard tab and Category: Macros. Click the New Macro Button and then search for Zoom 1 to 1.swp (If you move the file to another location, you will have to locate it again.) <Capture3.jpg>
I don't know if anyone else likes to see their parts in real size, but this is a handy solution that doesn't take long to set up and now I can instantly zoom any part or assembly (haven't tried a drawing yet) to real size on my screen with Ctrl+M.