The DC voltage drop is simpler because it does not have to consider an AC power factor. On an AC circuit, if the power factor is not 1, then the effects of reactance must be considered (as well as the resistance).
For a DC circuit, a simple calculation of voltage drop would be:
VD = R X CL/1000 X A
where:
R = Resistance of wire (Ohms) per 1000 feet
CL = Circuit Length (distance out to load and back)
A = Total Circuit Load in Amperes
If your wire R value is per 100 feet, then change the 1000 divisor to 100.
You can see that the voltage drop is dependent on how heavy the circuit is loaded (not just the size of the wire and the length). This is a fact often forgotten or ignored.
For an AC single-phase circuit, for "R" in the above formua you have to substitute the effective "Z" (Impedance = Resistance + Reactance) for the circuit power factor.