The default value for font and basefont sizes in HTML is 3. If you want to have your text displayed in a larger or smaller font relative to the basefont, you can prefix the value with a plus (+) or minus (-) character. Thus, to specify a font size that is two times larger than the basefont, use the following syntax:
<FONT size="+2">Your text here.</FONT>
To specify a font size that is two times smaller than the basefont, use the following syntax:
<FONT size="-2">Your text here.</FONT>
NOTE: The basefont is essentially the default font size that a browser uses to render the text when your site is visited. Therefore if a site visitor sets the default font size to a value larger or smaller than the default basefont of 3, the text may appear much larger or smaller than intended. This option may not be available in all web browsers.