Several factors influence the selection of cable thickness, including:
"We need #4 THHN. 185 feet. And I’m going to need to cut a new trench to the panel." electrical cable thickness calculator
But the calculator also showed him the why . He clicked "Show math." Several factors influence the selection of cable thickness,
$$A_{vd} = \frac{2 \times I \times L \times \cos\phi}{\sigma \times \Delta V_{max}}$$ electrical cable thickness calculator
"Not yet!" he shouted back, spitting out the flashlight.
The amount of power your devices will draw.