Following is a handy matrix for those among us who like to indicate HTML (font) sizes in “em”s. All modern browsers use a 16px default font size. Specifying the font-size and line-height in ems (relative to the 16px default font) allows the user to resize the font in the browser and produces the most consistent results across different browsers.

For more about using em’s, read:

Now, the matrix:

 font-size: .625em;            = 10px 
 font-size: .6875em;           = 11px 
 font-size: .75em;             = 12px 
 font-size: .8125em;           = 13px 
 font-size: .875em;            = 14px
 font-size: .9375em;           = 15px
 font-size: 1.0625em;          = 17px
 font-size: 1.125em;           = 18px     
 font-size: 1.188em;           = 19px      
 font-size: 1.25em;            = 20px   
 font-size: 1.313em;           = 21px        
 font-size: 1.375em;           = 22px         
 font-size: 1.438em;           = 23px         
 font-size: 1.5em;             = 24px
 font-size: 1.563em;           = 25px         
 font-size: 1.625em;           = 26px          
 font-size: 1.688em;           = 27px         
 font-size: 1.75em;            = 28px         
 font-size: 1.813em;           = 29px          
 font-size: 1.875em;           = 30px