How to calculate cable diameter?

I am trying to figure out how large of an opening to my connector I will need. I have 12 circuits comprised of a V+, GND, Data+, and Data-. The V+ and GND are going to be either 16 AWG or 14 AWG and the Data lines are both going to be 24 AWG.

I realize I could get an approximate answer just by taking the area of the different gauge wires, multiplying that by the number of wires I have, and then finding a circle with the same area. This is cruder than I would like. I know there is a term for the correction factor I am looking for but all of the terms I am searching for provide fruitless results. This would be similar to a packing problem I guess.

Thanks for any help you offer!