Display width: Sysmetric(1)
Display height: Sysmetric(2)
Intellisense tells you these are screen width and height. Well, in tho loose sense of screen=display, not _SCREEN=screen.
What's less often discussed is that the area you have for your app can be smaller, if the toolbar is shown. There are two symmetric calls that take that into account and give you the size a maximised form will have as Sysmetric(21) and Sysmetric(22).
You can also get more details, take a look at what intellisense options pop up, when you type Sysmetric and the opening bracket.
Chriss