Just read interesting article on Smashing magazine regarding best practicies in website typography.
Conclusion:
The study shows a clear set of common practices and guidelines for setting type in Web design. Note, though, that these findings are not scientific and should serve only as rough guidelines:
- Either serif or sans-serif fonts are fine for body copy and headings, but sans-serif fonts are still more popular for both.
- Common choices for headlines are Georgia, Arial and Helvetica.
- Common choices for body copy are Georgia, Arial, Verdana and Lucida Grande.
- The most popular font size for headings is a range between 18 and 29 pixels.
- The most popular font size for body copy is a range between 12 and 14 pixels.
- Header font size ÷ Body copy font size = 1.96.
- Line height (pixels) ÷ body copy font size (pixels) = 1.48.
- Line length (pixels) ÷ line height (pixels) = 27.8.
- Space between paragraphs (pixels) ÷ line height (pixels) = 0.754.
- The optimal number of characters per line is between 55 and 75, but between 75 and 85 characters per line is more popular,
- Body text is left-aligned, image replacement is rarely used and links are either underlined or highlighted with bold or color.
Read full article here: Typographic Design Patterns and Best Practices