Voltage Drop Calculator
Estimate round-trip conductor drop from a supplied resistance value.
Calculate drop without an invented wire table
Voltage drop in a two-conductor DC circuit equals round-trip conductor resistance times current. Rather than embedding a code-dependent wire table, this calculator asks for the conductor's resistance per kilometer, one-way length, current, and source voltage. That keeps material, gauge, stranding, and temperature choices explicit while reporting drop, load voltage, and source-voltage percentage.
For a 30 meter one-way run carrying 10 amperes through conductor rated 5 ohms per kilometer, the round-trip resistance is 0.3 ohm and drop is 3 volts. From a 120 volt source, predicted load voltage is 117 volts and drop is 2.5 percent. Enter resistance for one conductor; the formula applies the return path factor of two.
Match resistance to conductor conditions
This is a steady DC resistive estimate. AC circuits can require impedance, power factor, reactance, phase count, and different conductor arrangements. Resistance also rises with conductor temperature, and permitted drop or ampacity comes from applicable design rules rather than this arithmetic. All values remain in your browser. Obtain resistance from a manufacturer or trusted standard for the actual conductor and operating condition.
Frequently Asked Questions
Why does the formula multiply length by two?
Current travels out and back through two conductors, so the resistive path is twice the one-way run.
Where do I get resistance per kilometer?
Use manufacturer data or an applicable conductor standard for the actual material, size, stranding, and temperature.
Does this handle three-phase AC?
No. It is a two-conductor resistive model and does not include phase geometry or reactance.
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