A pica is equivalent to 12 points; thus, there are 6 picas per inch. You can try to run the following code to set font size using pica (pc):
Example
<html> <head> </head> <body> <div style = "position:relative;left:10px;top:3px;background-color:yellow;font-size:3pc;"> This div has font size set in pica. </div> </body> </html>