Sri has shown approximate figures rounded off to the nearest manufacturing measurements. Cables are manufactured to some standard measurements to suit die size, costs, and other factors.
For example AWG 12 is exactly 3.310mm x 3.310mm, but nobody may be manufacturing to these specifications. So you choose a size rounded off to the nearest 0.5 or 1.0. You can use either a 3mmx3mm or 4mmx4mm squared. Since the exact specs are more than 3mmx3mm, you choose 3.5x3.5 and if that is not available choose 4x4.