According to this page, it seems most of recent browsers use the same value for line-height: normal : 1.14, id est the font-size property with a 1.14 coefficient.
Tried with several browsers (on Windows XP) :
- Chrome 21.0.1180.75
- Firefox 14.0.1
- Safari 5.1.7
- Opera 11.64
- IE 7
- IE 8
EDIT
I was wrong, line-height depends of font-family, font-size, your browser, maybe your OS…
More reading on Eric Meyers’ website.