You might look at the following articles on MSDN:
http://support.microsoft.com/default...b;en-us;127152
If you're not as picky as the above article, you can always use the
DpiX and DpiY properties of the Graphics object on which you're
drawing. (You must always determine pixels to inches based on some
output device... the conversion is meaningless in the absence of a
graphics context of some kind.) In DpiX and DpiY, the "D" stands for
"dots" or pixels, while the "i" stands for "inches". So, you can
convert pixels to inches. Then all you have to do is convert inches to
centimeters.