To me it's a matter of a few things:
- flow.. how the scenes flow together and what makes them one logical unit
- plot... a chapter should have some kind of arc, if you will, or beginning-middle-end
- length... I tend to not like my chapters become too long
I don't think there's a science to it. You have to look at your own work and make that judgment. Sometimes my chapters are 1 page long, and sometimes they're 15 pages. But I use those three criteria and it becomes an intuition to me.
Also, if you look at my first novel, TPB, and the first half of the book -- every chapter seems to have some kind of conclusion, a nice unit of beginning-middle-end, if you will. It makes for a more leisurely pace. But in the second half of the book, the pace speeds up and I often ends the chapters with some kind of "cliffhanger." The result is that my readers found it harder to put down the book -- at the end of the chapter (which would be a good place to stop), they'd want to turn the page to find out what happened next. So that's definitely a good way to end a chapter, if that's what you want to accomplish (but still, even chapter should be a logical unit and collection of scenes).
Also, I don't worry about chapter breaks in first drafts.