The Voltage Drop Calculator computes the voltage lost along a known wire run. Enter the conductor size, current, one-way length, material, system voltage and phase to get the drop in volts and as a percentage.
Voltage Drop Calculator
Calculate voltage drop in volts and percent for a known wire size, current, length and material. Supports single and three phase, copper and aluminum.
Inputs
Result
--
voltage drop (V)
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drop percent
About Voltage Drop Calculator
Features
- Works for any standard AWG or kcmil
- Single and three phase
- Copper or aluminum
- Reports volts and percent drop
How to Use
- Pick wire size, material, phase and voltage.
- Enter current and one-way length.
- Read the voltage drop in volts and percent.
Examples
Example: 8 AWG copper, 50 A, 100 ft, 240 V single phase -> 6.3 V (2.6%).
Benefits
- Check an existing or planned run
- Decide if a larger wire is needed
Frequently Asked Questions
What is voltage drop?
It is the loss of voltage along a wire caused by its resistance. Too much drop wastes energy and can make equipment misbehave.
How is it calculated?
Single phase: VD = 2 x I x R x L. Three phase: VD = sqrt(3) x I x R x L. I is current, R resistance per length, L one-way length.
What is an acceptable drop?
NEC recommends a maximum of 3% on branch circuits and 5% total. Below 3% is ideal.
Do I need both conductors?
Yes. Single-phase runs use the round-trip length (two wires), which is why the factor is 2.
Is my data saved?
No. Everything is computed in your browser.