I’ve had some issues recently trying to get a fieldset pixel perfect, some things just didn’t add up (and I’m not just talking about the height and things overlapping here).
So I thought I’d make some notes on the subject:
The first place to start is the box model, a height of 100px is the inner height, the border, the legend text size and its padding are additional to this. I really hadn’t given any thought to the legend having padding!
Another thing to note is the border size isn’t consistent across browsers.