There are no standard web font sizes, and there are no best fonts either. In fact, it is better if the font size is not fixed so people can make adjustments and make text easier to read.
Why are there no Standard Fonts for the Internet?
The reason is people use different programs and settings to access the Net. There are also different programs used to create web pages. These reasons make it impossible to have a certain font size set as the standard.
How to Specify Font Size
The font should be set using EMI (with external CSS files) or in percentages. Using either of these methods will allow people to adjust the font according to their own preference. Graphics of text should be avoided; they are impossible to scale up or down.
No matter what system you use (i.e., Mac, Windows, Linux etc), only a few fonts are likely to be installed. Of course you can always download more on the web.
Also, most browsers allow users to decide what fonts to use for viewing web pages. You can even suggest fonts if you use CSS. But never assume that a font will be available for a user no matter how popular it is.
The lack of a standard web font size means your web page must be adaptable. If you look at the same font type and size on Windows and the Mac, the one on the Mac will always be smaller. This is because the Mac resolution is 72 dpi while for Windows it is 98 dpi.
Avoid Small Fonts
Research shows that many people have trouble reading fonts smaller than 14 pts on newspapers. It’s even harder to read on the monitor because of the lower resolution. Rather than use points or pixels for fonts, don’t specify a font size for the BODY in CSS.
Not doing this will allow a user to select the font point level they are comfortable with. You should also set level 1 headings to be 30% bigger than the body text. Make level 2 20% bigger than the body text, etc. This way, the heading size will increase in proportion to the body text.
The bottom line is this: there are no standard web font sizes. But even so, it is a good idea to avoid using very small fonts. Remember, if the fonts are too small, the reader will be turned off and go to another site.