what you explained is already right. i had already worked with all formulas mentioned above. however, it takes too much time just to calculate ampacity through all of those criteria (DC resistance, ac resistance, skin effect, etc.). when we work on planning some systems, i think there is an easier way to calculate the ampacity from the cross area section vice versa so that we don't spend much time calculating and need not to carry the rating table all the time.
i would like to know what formula it is.