Typography is very important for websites, mainly because is the best way to help users to read easily and to focus on the important parts of the text. Another aspect of the typography is that it makes the text beautiful and can give the user the needed mood to read and understand the message.
Here is a quick research on what fonts and font sizes are using some of the best known websites by designers:
Apple is using Lucida Grande and Lucida Sans Unicode as primary fonts, starting with a font size of just 10px for the footer links, 12px for some elements like the secondary menu, 14px – 16px for paragraphs and 22px – 24px for most of the headings, excepting those displayed as pictures.
Google is a lot more classy, using Arial as primary font and small font sizes (12-13px). Even YouTube is using the same standards. Other Google pages are using another font: open sans and more appealing headings and styles.
This well known website uses Proxima Nova with fallback to Helvetica Neue and Arial. The headings font is Skolar. The font size for paragraphs is 16px, and 32px for the headings.
Twitter is using Helvetica Neue with Arial fallback for the content pages. The most common font sizes are 14px and 16px for paragraphs and 40px – 20px for headings.
Graphicriver as well as other Envato websites is more conservative by using Tahoma and small fonts (13px) for paragraphs, but for the big headings is using ProximaNovaSoft font and 38px size, while other headings have 24px and Helvetica Neue.