Voltage Drop Calculator — Wire Size, Length & Load | koeedmro
TOOL
Voltage Drop Calculator
How It Works
Standard DC resistance per conductor size at 75°C, two-wire formula for single-phase and √3 for three-phase. Keep branch-circuit drop at or below 3% — feeder + branch combined at or below 5%. Failing runs call for a larger conductor or shorter run.
Verify against the NEC and local codes — this calculator is a sizing aid, not a substitute for code-compliant design.
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FAQ
What is an acceptable voltage drop?
3% or less for a branch circuit, 5% or less for feeder plus branch combined. Sensitive equipment may need tighter limits — check the specification and local code.
Does it include temperature correction?
Values are at 75°C. High-ambient or bundled runs run hotter and drop slightly more — allow margin.
Aluminum vs copper?
Aluminum conducts ~60% as well as copper by size — typically two to three AWG sizes larger for the same drop and ampacity.