How to find the comparative object's position compare with game screen?

As the title, I don’t know how to define the comparative object’s position in script. For example, in my scene, my gameObject has the Vector3 like this: x=1000, y=0, z =500, then how can I find out the Vector2 of this gameObject compare with the screen width and screen length?
Sorry for my bad English.

Camera.main.WorldToScreenPoint (and there are a couple more helper methods like that on Camera class).