You need to find the area of the wire. Just using 12 "units" as the diameter because it's 12 AWG.
Area = pi times Radius squared
pi(12)^2 = 452.41 units
pi(6)^2 = 113.10 units
The 6awg is 4 times as big as the 12awg as the area of a circle increases expodentially.
To find twice the size of 12awg, take the area, 113.10, and multiply it by 2. Then take the resulting 226.2 and divide it by pi. You'll get about 72. Find the square root of 72 and that's the gauge wire that is double 12awg.
If my assumptions are correct, twice the size of 12awg is 8.51awg. So 7 or 8 gauge wire will be twice the size of 12awg.
Yes, I do feel pretty cool.
