Voltage Drop Calculator

Ohm's law voltage drop.

Choose a voltage-drop methodUse measured circuit resistance or size a copper/aluminum conductor by AWG, phase, and one-way run.

4 options

Load current

Circuit resistance

Resistance unit

Source voltage

VOLTAGE DROP2 V

I × total circuit resistance; circuit resistance 0.2000 Ω. Drop 1.67%; load voltage 118.000 V.

Estimate based on the values shown

Formula checkedKnown resistance uses Vdrop = I×R. Conductor mode uses standard circular-mil AWG area and K=12.9 copper or 21.2 aluminum Ω·cmil/ft; single-phase uses 2KIL/CM and three-phase uses √3KIL/CM. Advanced workflows include conduit/cable installation, parallel conductors, power factor, direct R/X or impedance, metric and long-distance runs, and resistance units.

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