John, physics was never my strong point in school so could you elaborate on your first line "The frequency is directly proportional to the tension, and inversely proportional to the weight."
When you speak of "weight" do you mean the number of pounds it requires to raise the string to the required pitch? Which would be the same as tension, wouldn't it?
D'Addario print the tensions at standard pitch on the packet, so there should be no problem calculating the total tension using the above formula. My feeling is that tuning the bass to C requires a heavy gauge string.