Voltage Drop Calculator

Calculate voltage drop in electrical wire runs.

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Voltage Drop Calculator

Voltage Drop Calculator

Voltage drop is the reduction in electrical potential (voltage) along a wire due to resistance. Excessive voltage drop causes equipment to malfunction, motors to overheat, and lights to dim. The NEC (National Electrical Code) recommends keeping voltage drop below 3% for branch circuits and 5% total for feeders plus branch circuits.

Common Uses

  • Sizing wire gauge for electrical circuits
  • Long-run wiring for outbuildings, RVs, and marine applications
  • LED lighting system design
  • Industrial motor circuit planning

Frequently Asked Questions

How is voltage drop calculated?
Voltage Drop = (2 × Length × Current × Resistance per foot) for DC circuits. For AC single-phase: VD = (2 × L × I × R) / 1000, where L = one-way length in feet, I = current in amps, R = resistance from conductor tables. Wire resistance increases with length and decreases with larger gauge.
What wire gauge should I use?
Common wire gauges and ampacity: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A, 8 AWG = 40A, 6 AWG = 55A. For long runs, go up one or two gauge sizes to keep voltage drop under 3%. Use our calculator to find the optimal gauge.
Is this calculator free to use?
Yes. All calculators on zenicalculator.com are completely free with no registration required.
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