How much of Transformers 3 is actually 3d?

I saw Harry Potter 6 in 3d, and most of it wasn't actually 3d, maybe
only 20 minutes of it. How much of Transformers 3 is actually shot in
3d?
I guess what I mean isn't how much is shot in 3d, but how much of the
film will you notice the 3d. The Harry Potter film I saw, we were
only told to put on our glasses for about 20 minutes of the film.