I am designing a web application, and I wish to know the largest size (x and y) that I can design for.
As of January 2008, about half of users are using 1024x278 screens, and probably less than 10% are using smaller screens. (Phone and palmtop users are an exception here.) So we are designing for minimum screen size of 1024x768.
However, that's the screen size, and when we are laying out our content we need to know the viewport size. There is evidence that most users have the browser maximized, but one still must subtract out space for OS decorations and browser chrome. People customize their chrome, so there is no single "right" answer; I am going for a reasonable bound that will accommodate the majority of users.
I see plenty of designers who say that they use a width of 960 pixels because it has many factors and can be divided up evenly -- but before deciding on this I want to know the maximum size that I can get away with, then I might choose to use somewhat less. I have seen max widths of 960, 974 or even 990 quoted... my own experiments seem to show a width of 1000 works OK.
Heights are even more difficult to come by: I find I can fit a vertical viewport height of 595 pixels works on the browsers that I've tried, with typical default OS and chrome settings. But I haven't tried very many, and I would rather see a more authoritative source. Surely someone else has done this research and done it better than me.
So my real question is this: What is the largest viewport size I can design for and expect it to fit without scrollbars for 80-90% of all users?