Predict the size of a UML class

[<eg_lwkae stu ust hk>]

Dear all,

   I am doing a project that generate a diagram (DIA format)
by input data about the dependency of classess. However,
i got problem on setup dependency between the class.

   Since the file format of DIA is easy to read, i got no problem
to create a dia document with "UML - Class" object only.  But if i want to create "UML - Dependency" object.  
Since i dont know the 
actual size of the "UML - Class" , the "UML - Dependenct" object wont attach the "UML - Class" object 
correctly.(I created the UML - Class object by giving the positon - "elem_croner" only)

   What is the font for the UML - Class used? and what is the ratio between the font size and the actual size 
in a DIA document?
   Or anyone give me some advise on how to solve the problem?

thx u very much!!