Voltage Drop Calculator
Check how much voltage you lose over a run. Uses the common K-factor method.
Estimate only. This is a quick check. Wire sizing has to meet the current code book and your AHJ. Ampacity, temperature, and fill rules are separate checks.
Result
Fill in your numbers and hit Calculate.
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How the math works
Single phase: VD = 2 x K x I x L / CM
Three phase: VD = 1.732 x K x I x L / CM
K = 12.9 copper, 21.2 aluminum (ohm-cmil per ft, approx.)
L = one-way length in feet, CM = circular mils of the wire
Percent drop = VD / source volts x 100Circular mil sizes are the standard AWG and kcmil values. A common design target is about 3% on a branch circuit and 5% total, which the NEC mentions in informational notes. Your specs or AHJ may say different.
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