Typically, for each manufacturing process you have a book of values, probably locked in that small floor safe behind you. The manufacturer might call this the Design Manual, the Process Manual or the Rulebook.

This is where you will look up the resistivities in terms of ohms-per-square for your material. In your book, this will be called either sheet resistivity or sheet rho. (The Greek letter rho is pronounced "row," as in "rho, rho, rho your boat" which only works in the English translation of this book, by the way. I can't wait to see how the translators handle that one.) The symbol for rho is ?.