I googled "Optimal font-size", read first 16 pixels then a dao of web design and came to the conclusion that the optimal font-size is not to specify one.


As for optimal line-height - around 1.5em is common, but The Golden Ratio seems a little neater. So that's a good standard.


As for line length - golden ratio typography claims that it should be proportional to line-height, which makes sense, but the equation they suggest just doesn't make any sense. A Smashing Magazine article suggests that around 65 characters per line is ideal, but that most people go for more like 75. 65em / 1.618 (golden) = 40.173 so I'm going to suggest that 41 times line height.