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I have half a meter of 18 AWG (1.02mm diameter) stranded copper wire and I am planning to run 12 volts with a maximum 6 amp load.

Determining the cross sectional area = 0.51mm^2 * PI, gives me ~8.17e-07 meters.

Determining the resistance R = (1.72e-8 * 0.5 meters) / area, gives ~0.0105 Ohms resistance for the half meter length.

My attempt to then determine voltage drop is V = I * R, V = 6 * 0.0105, giving a voltage drop of ~0.063 (~11.94V)

Why then do many online calculators have a multiplier of 2 on this drop? (~11.87V)

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Why then do many online calculators have a multiplier of 2 on this drop, ~11.87 V?

Because most circuits have a return wire.

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